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Purpose: The PRESTIGIO Registry was established in 2017 to collect clinical, virological and immunological monitoring data from people living with HIV (PLWH) with documented four-class drug resistance (4DR). Key research purposes include the evaluation of residual susceptibility to specific antiretrovirals and the validation of treatment and monitoring strategies in this population., Participants: The PRESTIGIO Registry collects annual plasma and peripheral blood mononuclear cell samples and demographic, clinical, virological, treatment and laboratory data from PLWH followed at 39 Italian clinical centres and characterised by intermediate-to-high genotypic resistance to ≥1 nucleoside reverse transcriptase inhibitors, ≥1 non-nucleoside reverse transcriptase inhibitors, ≥1 protease inhibitors, plus either intermediate-to-high genotypic resistance to ≥1 integrase strand transfer inhibitors (INSTIs) or history of virological failure to an INSTI-containing regimen. To date, 229 people have been recorded in the cohort. Most of the data are collected from the date of the first evidence of 4DR (baseline), with some prebaseline information obtained retrospectively. Samples are collected from the date of enrollment in the registry., Findings to Date: The open-ended cohort has been used to assess (1) prognosis in terms of survival or development of AIDS-related or non-AIDS-related clinical events; (2) long-term efficacy and safety of different antiretroviral regimens and (3) virological and immunological factors predictive of clinical outcome and treatment efficacy, especially through analysis of plasma and cell samples., Future Plans: The registry can provide new knowledge on how to implement an integrated approach to study PLWH with documented resistance to the four main antiretroviral classes, a population with a limited number of individuals characterised by a high degree of frailty and complexity in therapeutic management. Given the scheduled annual updates of PLWH data, the researchers who collaborate in the registry can send study proposals at any time to the steering committee of the registry, which evaluates every 3 months whether the research studies can be conducted on data and biosamples from the registry and whether they are aimed at a better understanding of a specific health condition, the emergence of comorbidities or the effect of potential treatments or experimental drugs that may have an impact on disease progression and quality of life. Finally, the research studies should aim to be inclusive, innovative and in touch with the communities and society as a whole., Trial Registration Number: NCT04098315., Competing Interests: Competing interests: RG reports payments to her institution from Gilead Sciences; personal fees for speaker panels and educational material from ViiV Healthcare, Merck Sharp and Dohme and Gilead Sciences and advisory boards from Theratechnologies, Janssen-Cilag and Gilead Sciences. FL reports personal fees for speaker panels from ViiV Healthcare, Janssen-Cilag and Merck Sharp and Dohme; travel grants from Gilead Sciences, ViiV Healthcare and Janssen-Cilag and advisory boards from ViiV Healthcare and Janssen-Cilag. EF reports personal fees for consultancy from Merck Sharp and Dohme, ViiV Healthcare, Gilead Sciences and Swedish Orphan Biovitrum; speaker panels and educational material from ViiV Healthcare and Gilead Sciences and advisory boards from ViiV Healthcare, Gilead Sciences and Merck Sharp and Dohme. ADB reports personal fees for speaker panels and educational material from ViiV Healthcare and Gilead Sciences and travel grants from ViiV Healthcare. AdCe reports personal fees for speaker panels from ViiV Healthcare. FM reports personal fees for consultancy and advisory boards from Merck Sharp and Dohme, ViiV Healthcare and Gilead Sciences. GM reports personal fees for speaker panels and educational material from Gilead Sciences; travel grants from Janssen-Cilag, Gilead Sciences and ViiV Healthcare and advisory boards from Gilead Sciences, ViiV Healthcare and Angelini Pharma. GC reports personal fees for speaker panels and educational material from Gilead Sciences, ViiV Healthcare and AbbVie and travel grants from Gilead Sciences. SR reports payments to his institution from Gilead Sciences, Janssen-Cilag and ViiV Healthcare; personal fees for travel grants from Gilead Sciences, Janssen-Cilag and ViiV Healthcare and advisory boards from Gilead Sciences, Janssen-Cilag, ViiV Healthcare and Merck Sharp and Dohme. MZ reports personal fees for consultancy and speaker panels and educational material from Gilead Sciences, ViiV Healthcare and Merck Sharp and Dohme. MMS reports personal fees for speaker panels and educational material from ViiV Healthcare, Merck Sharp and Dohme and Janssen-Cilag and advisory boards from ViiV Healthcare and Theratechnlogies. VS reports grants from Gilead Sciences and personal fees for speaker panels from Gilead Sciences, ViiV Healthcare and Merck Sharp & Dohme. AnCa reports personal fees for advisory boards, speaker panels and educational materials from Gilead Sciences, ViiV Healthcare, Janssen-Cilag, Merck Sharp & Dohme and Theratechnlogies. PRESTIGIO Registry received funding from Gilead Sciences, ViiV Healthcare, Merck Sharp & Dohme, and Theratechnologies.All other authors: no potential conflicts., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Hepatitis B virus (HBV) is a genetically diverse blood-borne virus responsible for chronic hepatitis B. The HBV polymerase plays a key role in viral genome replication within the human body and has been identified as a potential drug target for chronic hepatitis B therapeutics. However, available nucleotide reverse transcriptase inhibitors only target the reverse transcriptase domain of the HBV polymerase; they also pose resistance issues and require lifelong treatment that can burden patients financially. In this study, various chemical classes are reviewed that have been developed to target different domains of the HBV polymerase: Terminal protein, which plays a vital role in the formation of the viral DNA; Reverse transcriptase, which is responsible for the synthesis of the viral DNA from RNA, and; Ribonuclease H, which is responsible for degrading the RNA strand in the RNA-DNA duplex formed during the reverse transcription process. Host factors that interact with the HBV polymerase to achieve HBV replication are also reviewed; these host factors can be targeted by inhibitors to indirectly inhibit polymerase functionality. A detailed analysis of the scope and limitations of these inhibitors from a medicinal chemistry perspective is provided. The structure-activity relationship of these inhibitors and the factors that may affect their potency and selectivity are also examined. This analysis will be useful in supporting the further development of these inhibitors and in designing new inhibitors that can inhibit HBV replication more efficiently., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Masson SAS. All rights reserved.)

Introduction: Combination antiretroviral therapy is currently the main component of treatment for human immunodeficiency virus (HIV) infected patients. At the same time, the high mutational potential of the virus and the frequency of side effects of existing drugs dictate the need for the development and preclinical study of new, more effective and safer compounds.The aim of the study is to evaluate the specific types of toxicity of a new non-nucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RNA-dependent DNA revertase) (NNRTI) based on the substance 1-[2-(2-benzoylphenoxy)ethyl]-6-methyluracil, a benzophenone derivative., Material and Methods: The study investigated reproductive toxicity, embryotoxicity, immunotoxicity, genotoxic (in micronucleus test in and comet assay) and allergenic properties of the test itemcompound. It was tested on three species of animals in two doses: the estimated therapeutic dose (1 TD) and its tenfold equivalent (10 TD). Taking into account the metabolic coefficients, the doses for rats (Rattus) were 9 and 90 mg/kg, for mice (Mus musculus), 21 and 210 mg/kg, and for guinea pigs (Cavia porcellus), 8 and 80 mg/kg, respectively., Results and Discussion: According to the obtained results, a favorable safety profile of the tested compound was established. Negative effects on the immune system, reproductive function, the body of pregnant animals and the fetus were not observed, as well as the compound did not have genotoxic and allergenic properties., Conclusion: These data allows to consider the studied compound as a promising therapeutic candidate for the treatment of HIV-1 infection.

Hepatitis B virus (HBV) is a hepatotropic, partially double-stranded DNA virus that replicates by reverse transcription and is a major cause of chronic liver disease and hepatocellular carcinoma. Reverse transcription is catalyzed by the four-domain multifunctional HBV polymerase (P) protein that has protein-priming, RNA- and DNA-dependent DNA synthesis (i.e., reverse transcriptase), and ribonuclease H activities. P also likely promotes the three strand transfers that occur during reverse transcription, and it may participate in immune evasion by HBV. Reverse transcription is primed by a tyrosine residue in the amino-terminal domain of P, and P remains covalently attached to the product DNA throughout reverse transcription. The reverse transcriptase activity of P is the target for the nucleos(t)ide analog drugs that dominate HBV treatment, and P is the target of ongoing efforts to develop new drugs against both the reverse transcriptase and ribonuclease H activities. Despite the unusual reverse transcription pathway catalyzed by P and the importance of P to HBV therapy, understanding the enzymology and structure of HBV P severely lags that of the retroviral reverse transcriptases due to substantial technical challenges to studying the enzyme. Obtaining a better understanding of P will broaden our appreciation of the diversity among reverse transcribing elements in nature, and will help improve treatment for people chronically infected with HBV., (Copyright © 2021 Elsevier Inc. All rights reserved.)

A linear quantitative structure activity relationship (QSAR) model is presented for predicting human immunodeficiency virus-1 (HIV-1) reverse transcriptase enzyme inhibition. The 2D QSAR and 3D-QSAR models were developed by stepwise multiple linear regression, partial least square (PLS) regression and k-nearest neighbor-molecular field analysis, PLS regression, respectively using a database consisting of 33 recently discovered benzoxazinones. The primary findings of this study is that the number of hydrogen atoms, number of (-NH2) group connected with solitary single bond alters the inhibition of HIV-1 reverse transcriptase. Further, presence of electrostatic, hydrophobic and steric field descriptors significantly affects the ability of benzoxazinone derivatives to inhibit HIV-1 reverse transcriptase. The selected descriptors could serve as a primer for the design of novel and potent antagonists of HIV-1 reverse transcriptase.

The pregenomic RNA (pgRNA) of hepadnaviruses serves a dual role: as mRNA for the core (C) and polymerase (P) synthesis and as an RNA template for viral genome replication. A question arises as to how these two roles are regulated. We hypothesized that the P protein could suppress translation of the pgRNA via its interaction with 5' stem-loop structure (epsilon or encapsidation signal). Consistent with the hypothesis, we observed up-regulation of the C protein level in the absence of the P protein expression in a physiological context. Importantly, translational suppression depended on the 5' epsilon sequence. Furthermore, the impact of the P protein on ongoing translation of the C ORF was directly demonstrated by polysome distribution analysis. We conclude that the P protein suppresses translation of the pgRNA via a mechanism involving its interaction with the 5' epsilon sequence, a finding that implicates the coordinated switch from translation to genome replication.

DNA microarray technology has been increasingly applied for studies of clinical samples. Frequently, RNA probes from clinical samples are available in limited amounts. We describe a reliable amplification method for bacterial RNA. We verified this method on mycobacterial RNA applying mycobacterial genome-directed primers (mtGDPs). Glass slide-based oligoarrays were employed to assess the quality of the amplification method. We observed a relatively small bias in amplified RNA pool when compared to the unamplified one. Up to 1000-fold linear RNA amplification in a single amplification round was obtained. To our knowledge, this study describes the first amplification method for mycobacterial RNA.

Throughout most of the past century, physicians could offer patients no treatments for infections caused by viruses. The experience with treatment of infection by human immunodeficiency virus (HIV) has changed the way healthcare workers deal with viral infections and has triggered a growing rate of discovery and use of antiviral agents, the first fruits of the expanding genomics revolution. HIV treatment also provides an informative paradigm for pharmacogenomics because control of infection and its consequences is limited by the development of viral drug resistance and by host factors. This report summarizes studies published to date on the significance of testing of HIV-1 resistance to antiretroviral drugs. The only Food and Drug Administration-approved kit is commercially available through Visible Genetics, Inc., for HIV drug resistance testing by genotypic sequencing. Genotyping sequencing alone is most likely an adequate test to assist in the therapeutic decision-making process in cases of previous regimen failure, treatment-naïve patients in areas of high prevalence of transmitted resistant virus, and pregnant women. However, in exceptional cases of highly complex mutation patterns and extensive cross-resistance, it may be useful to obtain a phenotype test, because that result may more easily identify drugs to which the virus is least resistant. There are no published clinical trial results on the usefulness of the so-called virtual phenotype over genotypic sequencing alone. The paradigm of viral pharmacogenomics in the form of HIV genotypic sequencing has been not only useful to the treatment of other viral diseases but also important to the real-life implementation of the growing discipline of genomics or molecular medicine. The application of this paradigm to the thousands of potential therapeutic targets that have become available through the various human genome projects will certainly gradually change the landscape of diagnosis and management of many diseases, including cancer.

Diverse mobile DNA elements are believed to pirate host cell enzymes to complete DNA transfer. Prominent examples are provided by retroviral cDNA integration and transposon insertion. These reactions initially involve the attachment of each element 3' DNA end to staggered sites in the host DNA by element-encoded integrase or transposase enzymes. Unfolding of such intermediates yields DNA gaps at each junction. It has been widely assumed that host DNA repair enzymes complete attachment of the remaining DNA ends, but the enzymes involved have not been identified for any system. We have synthesized DNA substrates containing the expected gap and 5' two-base flap structure present in retroviral integration intermediates and tested candidate enzymes for the ability to support repair in vitro. We find three required activities, two of which can be satisfied by multiple enzymes. These are a polymerase (polymerase beta, polymerase delta and its cofactor PCNA, or reverse transcriptase), a nuclease (flap endonuclease), and a ligase (ligase I, III, or IV and its cofactor XRCC4). A proposed pathway involving retroviral integrase and reverse transcriptase did not carry out repair under the conditions tested. In addition, prebinding of integrase protein to gapped DNA inhibited repair reactions, indicating that gap repair in vivo may require active disassembly of the integrase complex.

Major T-cell receptor beta chain variable region (TCRBV) repertoire perturbations are temporally associated with the down-regulation of viremia during primary human immunodeficiency virus (HIV) infection and with oligoclonal expansion and clonal exhaustion of HIV-specific cytotoxic T lymphocytes (CTLs). To determine whether initiation of antiretroviral therapy (ART) or highly active antiretroviral therapy (HAART) during primary infection influences the dynamics of T-cell-mediated immune responses, the TCRBV repertoire was analyzed by semiquantitative polymerase chain reaction in serial blood samples obtained from 11 untreated and 11 ART-treated patients. Repertoire variations were evaluated longitudinally. Stabilization of the TCRBV repertoire was more consistently observed in treated as compared with untreated patients. Furthermore, the extent and the rapidity of stabilization were significantly different in treated versus untreated patients. TCRBV repertoire stabilization was positively correlated with the slope of HIV viremia in the treated group, suggesting an association between repertoire stabilization and virologic response to treatment. To test whether stabilization was associated with variations in the clonal complexity of T-cell populations, T-cell receptor (TCR) heteroduplex mobility shift assays (HMAs) were performed on sequential samples from 4 HAART-treated subjects. Densitometric analysis of HMA profiles showed a reduction in the number of TCR clonotypes in most TCRBV families and a significant decrease in the total number of clonotypes following 7 months of HAART. Furthermore, a biphasic decline in HIV-specific but not heterologous CTL clones was observed. This indicates that ART leads to a global reduction of CD8(+) T-cell oligoclonality and significantly modulates the mobilization of HIV-specific CTL during primary infection. (Blood. 2000;95:1743-1751)

Human immunodeficiency virus (HIV) and Kaposi's sarcoma-associated herpesvirus (KSHV) coinfect many individuals in North America and in parts of Africa. Infection with HIV is a leading risk factor for the development of Kaposi's sarcoma (KS). In this study, we tested the hypothesis that HIV infection of common or adjacent cells would stimulate replication and spread of KSHV. Infection of a primary effusion lymphoma cell line by vesicular stomatitis virus type G-pseudotyped HIV type 1 led to a rapid induction of lytic-phase KSHV replication. Induction of lytic KSHV replication by HIV required active replication of HIV. The addition of the nucleoside reverse transcriptase inhibitor azidothymidine or the protease inhibitor indinavir to the culture prevented HIV spread and inhibited the associated induction of KSHV lytic replication. Lytic replication occurred in both HIV-infected and HIV-uninfected cells within the culture, and could be induced in uninfected cells via a soluble factor released from the HIV-infected cells. Transmission of infectious KSHV to an uninfected target cell was enhanced by HIV replication and was inhibited by antiretroviral drugs. These results may have implications for the pathogenesis and treatment of KS in individuals coinfected with KSHV and HIV.

Numerous instances of reverse transcriptase (RT) inhibition of the PCR were observed while developing nonquantitative uncoupled RT-PCR techniques for detecting nitrogenase and ammonia monooxygenase gene expression in situ. The inhibitory effect of RT on the PCR was removed with increasing template concentrations beyond 10(5) to 10(6) copies. Including T4 gene 32 protein during the reverse transcription phase of the RT-PCR reaction increased the RT-PCR product yield by as much as 483%; if gene 32 protein was introduced after reverse transcription but prior to the PCR phase, no improvement in product yield was observed. Addition of 1 microgram of exogenous calf thymus DNA or yeast tRNA did little to relieve RT inhibition of the PCR on both genomic DNA and mRNA templates. These results suggest that RT inhibition of the PCR is mediated through direct interaction with the specific primer-template combination (DNA and RNA) and point to specific assay modifications for estimating the extent of RT inhibition and counteracting some of the inhibitory effect. Furthermore, the working hypothesis of RT inhibition below a 10(5) to 10(6) copy threshold has important implications for quantitative RT-PCR studies. In particular, competitive, quantitative RT-PCR systems will consistently underestimate the actual RNA concentration. Hence, enumerations of RNA templates below 10(5) to 10(6) copies will be relative to an internal standard and will not be an absolute measure of RNA abundance in situ.

The tetramer of ethylenesulfonic acid (U-9843) is a potent inhibitor of HIV-1 RT* and possesses excellent antiviral activity at nontoxic doses in HIV-1 infected lymphocytes grown in tissue culture. Kinetic studies of the HIV-1 RT-catalyzed RNA-directed DNA polymerase activity were carried out in order to determine if the inhibitor interacts with the template primer or the deoxyribonucleotide triphosphate (dNTP) binding sites of the polymerase. Michaelis-Menten kinetics, which are based on the establishment of a rapid equilibrium between the enzyme and its substrates, proved inadequate for the analysis of the experimental data. The data were thus analyzed using steady-state Briggs-Haldane kinetics assuming that the template: primer binds to the enzyme first, followed by the binding of the dNTP and that the polymerase is a processive enzyme. Based on these assumptions, a velocity equation was derived which allows the calculation of all the specific forward and backward rate constants for the reactions occurring between the enzyme, its substrates and the inhibitor. The calculated rate constants are in agreement with this model and the results indicated that U-9843 acts as a noncompetitive inhibitor with respect to both the template:primer and dNTP binding sites. Hence, U-9843 exhibits the same binding affinity for the free enzyme as for the enzyme-substrate complexes and must inhibit the RT polymerase by interacting with a site distinct from the substrate binding sites. Thus, U-9843 appears to impair an event occurring after the formation of the enzyme-substrate complexes, which involves either an event leading up to the formation of the phosphoester bond, the formation of the ester bond itself or translocation of the enzyme relative to its template:primer following the formation of the ester bond.

Although detection of hepatitis C virus RNA with polymerase chain reaction has become the standard for diagnosis, extensive application has been thwarted by polymerase chain reaction's labor intensiveness, risk of false-positive results through contamination and time required for individual assays. To minimize these limitations, we developed and validated a one-step hepatitis C virus RNA polymerase chain reaction assay. The one-step method was compared with traditional hepatitis C virus RNA polymerase chain reaction using primers from the highly conserved 5' untranslated region of the hepatitis C virus genome. Variables studied in the one-step method included the source and quantity of reverse transcriptase (RTase), the concentration of MgCl2 and the duration of reverse transcription and complementary DNA amplification cycles. Optimal conditions for the one-step method were obtained with 25 U of reverse transcriptase and 2 mmol/L MgCl2. The one-step method substantially reduced the time required for analysis. The sensitivity of the one-step method was comparable to that of traditional hepatitis C virus RNA polymerase chain reaction using serially diluted RNA extracted from the serum of a hepatitis C virus-infected patient. The specificity of the one-step method was confirmed on Southern-blot hybridization. The results exhibited 100% concordance with results of traditional hepatitis C virus RNA polymerase chain reaction in 50 serum samples, including those of positive and negative controls. In addition, 100% concordance was observed between the two methods' results when sera containing low levels of hepatitis C virus RNA were used.(ABSTRACT TRUNCATED AT 250 WORDS)

The action of DNA polymerase (Sequenase Version 2.0) on an oligonucleotide template containing a 7-bromomethyl-benz[a]anthracene-deoxyadenosine adduct flanked by thymidine residues was investigated. The polymerase incorporated deoxyadenosine or deoxyguanosine residues opposite the thymidine 3' to the adduct with similar efficiencies. Whereas the normal A.T base pair led to arrest of polymerase progression along the template, formation of the G.T mismatch allowed incorporation of thymidine opposite the adduct and further primer extension. This mispair-mediated bypass was also seen with AMV reverse transcriptase and may represent a novel mechanism for overcoming the replication block of a bulky carcinogen--DNA adduct.

N-(Deoxyguanosin-8-yl)-2-(acetylamino)fluorene (AAF-G) adducts in the DNA of bacteriophage M13 can be converted to N-(deoxyguanosin-8-yl)-2-aminofluorene (AF-G) adducts in situ by treatment with 1.0 M NaOH for 45 min at room temperature. The conversion is accompanied by a dramatic increase in the transfection activity of the samples which is correlated with the measured deacetylation of the acetylaminofluorene adduct. The pair of substrates (AAF-G/AF-G) with adducts at identical places in the DNA has been used to study bypass synthesis catalyzed by T7 DNA polymerase, an altered T7 DNA polymerase from which the 3'----5' exonuclease has been genetically removed by an 84 nucleotide deletion (Sequenase 2), T4 DNA polymerase and Escherichia coli DNA polymerase I. All polymerases appear blocked at acetylaminofluorene lesions. Sequenase 2 is apparently able to add nucleotides opposite the acetylaminofluorene lesion but is unable to catalyze further elongation. T7 DNA polymerase, including thioredoxin and with an active 3'----5' exonuclease, is unable to bypass aminofluorene adducts, whereas Sequenase 2 bypasses the lesions readily. The data support the view that the elongation step is rate limiting in synthesis past lesions and that low 3'----5' exonuclease activity allows the priming nucleotide opposite the altered template site to remain in position long enough for elongation past particular adducts.

A novel enzyme inhibitor against RNA-directed DNA polymerase of avian myeloblastosis virus was produced by an isolate of a new streptomycete for which the name Streptomyces retrostaticus is proposed. This enzyme inhibitor, which was named retrostatin, did not inhibit DNA-directed DNA polymerase of Escherichia coli and DNA-directed RNA polymerase of Ehrlich ascites tumor cells. Retrostatin was produced by the microorganism together with streptonigrin. These two substances were extracted from the culture broth with ethyl acetate at acidic pH. Retrostatin is an acidic pH indicator and the free acid was recovered as a red powder. Retrostatin had weak antibiotic activities against Gram-positive bacteria and yeasts.

Induction of human fibroblast cells with poly rI.rC induces interferon mRNA which can be translated into interferon precursor in wheat germ cell free system or in Xenopus oocytes into biologically active interferon. The extent of gene expression in the poly rI.rC induced cells was compared to that of the uninduced cells by hybridization of the mRNA to complementary DNA. Homologous template driven hybridization of cDNA revealed the presence of two clearly defined transitions in the total poly A RNA from the induced cells; abundant class and a scarce class comprising approximately 37,000 diverse species of RNA. Heterologus hybridization of the cDNA with total uninduced mRNA showed that the majority of the mRNA sequences are the same in both the induced and uninduced cells. The results of the hybridization using cDNA prepared to the fraction enriched for interferon mRNA, however, showed that about 4% of the sequences present in the interferon enriched fraction are not present in the uninduced cells. These differences may result from the poly rI.rC induced alterations in gene expression.

Recent immunologic and microbiologic evidence suggests that urothelial tumors may be caused by "C" type oncogenic viruses. Such viruses may exert their oncogenic potential in responce to stimulation by known chemical carcinogens. By means of a unique enzyme, reverse transcriptase, these viruses are able to incorporate genetic information into that of the host, and can thereby be transmitted vertically from generation to generation. An evaluation of the specific antiviral agents dimethylbenzyldemethl-rifampicin and streptovaricin-comples, which inhibit the enzyme reverse transcriptase, revealed no depay in the induction of bladder tumors by the chemical carcinogen, 2-formylamino-4-(5-nitro-2-furyl) thiazole (FANFT) in C3H mice. This observation suggests that the reproduction and release of virus may not be essential in the malignant transformation of bladder epithelial cells, but does not preclude the possiblity that inherited viral genetic information may be involved in the oncogenesis of bladder tumors.

An inhibitor of reverse transcriptase of Moloney leukemia virus was reported previously in the cytoplasm of the cultured cells (1). In this report, the mechanism of the inhibition was examined. The inhibitory activity was completely abrogated by treatment at 55 degrees C for 20 min. Destruction of the reaction products of reverse transcriptase was not observed. Strong inhibition was observed by preincubation of poly rA oligo dT used as a template-primer, together with the inhibitor, but was not by incubation of poly rA or oligo dT with the inhibitor separately. It is suggested that the inhibitor reacts with poly rA oligo dT complex and interferes with attachment of the reverse transcriptase to the template-primer complex.

Terminal deoxynucleotidyl transferase (TdT) was used to prepare copolymers of dA and 1,N6-ethenodeoxyadenosine (epsilon dA). When used as templates for Escherichia coli DNA polymerase I (Pol I) and compared with poly (dA), normal dTTP incorporation was not significantly affected by the presence of 7% epsilon dA. dGTP misincorporation was only slightly increased and occurred about once for every 500 epsilon dA residues. The error-prone polymerase from avian myeloblastosis virus (AMV reverse transcriptase) increased this error rate 5- to 20-fold to a maximum of 1 dG/25 epsilon dA. No dCTP misincorporation was detected with either polymerase. In transcription with E. coli DNA-dependent RNA polymerase, no errors were revealed by nearest neighbor analysis. Poly (dA) treated with chloroacetaldehyde under conditions producing the same proportion of epsilon dA (without the hydrated form) as the synthesized template behaved in the same manner with a similar low level of misincorporation of dG. Such treatment of alternating poly d(A-T) caused structural changes indicative of crosslinks but did not alter its template properties. Increasing the amount of epsilon dA in either synthesized or modified polymers greatly decreased the template activity without increasing the error rate. It is suggested that epsilon dA generally does not prevent dT incorporation but behaves as a bulky lesion which is bypassed. In contrast to the low mutagenic efficiency of epsilon dA, O4-methyldeoxythymidine (m4dT), in copolymers with dA, directed the misincorporation of 1 dG/12 m4dT with Pol I and 1 dG/3 m4dT with reverse transcriptase. Nearest neighbor analysis of transcripts showed the incorporation of 1 dG/12 m4dT. These data are in agreement with the previous reported mutagenicity of m4dT in alternating poly d(A-T, m4T).

Human placental extracts contain a specific inhibitor of mammalian retroviral RNA-directed DNA polymerase (deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7) activity. This inhibitor copurifies with retrovirus-like particles in human placental extracts. The inhibitor can be removed from these particles by salt extraction, which leads to the recovery of the polymerase activity. Thus, the inhibitor does not irreversibly inactivate the particle-associated RNA-directed DNA polymerase activity. The inhibitory preparation contained no nuclease, protease, or phosphatase activity. Because its inhibitory action can be eliminated by the addition of more virus to the reaction, nonspecific inactivation of enzyme substrate has been ruled out. A partial characterization of the inhibitor indicates that it is (i) insensitive to ether, trypsin, and phospholipase C; (ii) stable to heat and pH 2-12; and (iii) nondialyzable.