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Three enzymes that cause inhibition of mRNA translation, eukaryotic initiation factor 2 protein kinase PK-i, oligoisoadenylate synthetase E, and phosphodiesterase 2'-PDi, have been recently isolated from interferon-treated cells. We show that the rise in these three enzyme activities may be used to study the response of uninfected cells to interferon. For each enzyme, a specific microassay that can be carried out on extracts from 2-5 x 10(4) monolayer cells from mouse, monkey, or man was developed. With these assays, the kinetics of induction of the three enzymes in mouse L cells are compared. The dose dependence for protein kinase PK-i induction is shown to be similar to that for the development of the antiviral state. Actinomycin D and anti-interferon serum block enzyme induction if added to the cells early after interferon treatment. The quantitative measurements of the intracellular level of these enzymes provide a new and convenient model to study the cell's response to interferon.

DNA from lambdagt-lambdaB bacteriophage was cleaved with EcoRI endonuclease and fragments from EcoRI-digested E. coli DNA were inserted. This DNA was used to infect E. coli, and phages containing the gene for DNA ligase were isolated by genetic selection. Two different hybrids were found with the same E. coli segment inserted in opposite orientations. Both hybrids produced similar levels of ligase as measured in crude extracts of infected cells.

A new protein retained by poly(I):poly(C)-Sepharose was induced together with dsRNA-dependent enzymatic activities, a protein kinase and 2',5'-oligoadenylate synthetase (2,5A synthetase), in interferon-treated mouse L929 cells; it had an apparent molecular weight of 50,000 (50 K) and was not phosphorylated by the protein kinase. The kinetics of the induction of the poly(I):poly(C)-binding 50 K protein were similar to those of dsRNA-dependent protein kinase and 2',5'-oligoadenylate synthetase, and their inductions were all dependent on the interferon dose added, though a relatively higher dose was required for the 50 K protein. When the interferon preparation was heated to 100 degrees C in the presence of sodium dodecyl sulfate, its effect on cells of inducing the activity of 2',5'-oligoadenylate synthetase was preserved completely, indicating that the interferon molecule itself is responsible for the induction of the synthetase. Since the induction of the enzymatic activity was inhibited by addition of either actinomycin D or cycloheximide, it may not be an activation of a latent enzyme but a de novo synthesis of the enzyme.

The expression of DNA ligase genes was studied using the nuclear transplantation approach in the germ line of Pleurodeles waltlii (P. waltlii) just before and during gonadogenesis. Germ cell (GC) nuclei were isolated from larvae of P. waltlii and transplanted into unfertilized Ambystoma mexicanum eggs. DNA ligase activity in these eggs was then analyzed after sucrose gradient fractionation. The activity of DNA ligase I (heavy form, 7.5 S) of P. waltlii was present when the transplanted GC nuclei were isolated before the first histological appearance of gonadogenesis. At the beginning of genital ridge formation and thereafter, DNA ligase I activity was replaced by that of DNA ligase II (light form, 7 S). Expression of form I was found to be sensitive to inhibitors of translation and transcription, while that of form II was not. Therefore, the change in DNA ligase activity of the transferred nuclei of P. waltlii germ cells was assumed to be the consequence of a change in gene activity, namely, the repression of the gene encoding DNA ligase I. This change in the gene-regulated state could be linked to protein modifications of the chromatin. These results indicate that, at the beginning of gonadogenesis, germ cells receive information leading to a new state of differentiation.

Temperature-sensitive (ts) mutants of the T4 phage rII gene were islated and used in temperature shift experiments that revelaed two different expressions for the normal rII (rII+) gene function in vivo: (i) an early expression (0 to 12 min postinfection at 30 C) that prevents restriction of T4 growth in Escherichia coli hosts lysogenic for gamma phage, and (ii) a later expression (12 to 18 min postinfection at 30 C) that results in restriction of T4 growth when the phage DNA ligase (gene 30) is missing. The earlier expression appeared to coincide with the period of synthesis of the protein product of the T4 rIIA cistron, whereas the later expression occurred after rIIA protein synthesis had stopped. The synthesis of the protein product of the rIIB cistron continues for several minutes after rIIA protein synthesis ceases (O'Farrell and Gold, 1973). The two rII+ gene expressions might require different molar ratios of the rIIA and rIIB proteins. It is possible that the separate expressions of rII+ gene function are manifestations of different associations between the two rII proteins and other T4-induced proteins that are synthesized or activated at different times after phage infection.

Strand breaks accumulated in the DNA of a temperature-sensitive DNA ligase mutant of Escherichia coli growing at the restrictive temperature, as detected by zone sedimentation through alkaline sucrose density gradients. The rate of strand breakage was increased by concomitant thymine starvation. Rifampicin and chloramphenicol inhibited the accumulation of strand breaks in the DNA. There was a correlation between the accumulation of strand breaks in the DNA and lethality, suggesting that such breaks are the basis for lethality at the restrictive temperature.

The recA1 mutation was transduced into the tag-2 mutant of E. coli, thus making a strain deficient in the induction of SOS repair as well as in the constitutive repair of 3-alkylated adenines in DNA. The double mutant recA tag is more sensitive to methyl methanesulfonate exposure than either single mutant, indicating that recA and tag mutations block different pathways in repair of alkylation damage. The double mutant is more deficient in host cell reactivation of alkylated phages than the tag single mutant. However, alkylation induction of the double mutant with N-methyl-N'-nitro-N-nitrosoguanidine resulted in killing adaptation of the cells to methyl methanesulfonate and restored the host cell reactivation capacity for alkylated lambda phage to wild-type levels. These adaptive responses can be ascribed to the induction of 3-methyladenine DNA glycosylase II which is shown by enzyme analysis to proceed normally in the recA mutant background. The results imply that the induction of the alkA gene encoding 3-methyladenine DNA glycosylase II is independent of SOS induction.

An oligonucleotide polymerase and a protein kinase which require double-stranded RNA (dsRNA) for activation are induced in HeLa cells by human fibroblast interferon. The polymerase synthesizes a series of oligonucleotides from ATP, whereas the kinase phosphorylates a polypeptide of Mr = 72,000 and the alpha subunit of initiation factor eIF-2. Partially or fully 2'-O-methylated derivatives of poly(inosinic acid) . poly(cytidylic acid) (rIn . rCn) were used to determine the structural requirements of dsRNA in the activation of these two enzymes. While fully methylated polymers failed to activate either enzyme, partially methylated polymers activated the enzymes in specific manners. The activation of the kinase by the rIn . rCn analogues was affected more severely by the level of methylation than was the activation of the polymerase. Moreover, fully methylated analogues blocked the activation of the kinase by rIn . rCn but not the activation of the polymerase. These observations are consistent with a biphasic model for enzyme activation similar to that proposed for interferon induction, which required the recognition of a relatively small region of rIn . rCn as the last step. Differences in the activation of the polymerase and kinase are explicable on the basis of the polymerase requirement for a smaller recognition region of the rIn . rCn duplex than the kinase. Dependence of polymerase activation on the level of methylation shows striking similarities with the interferon inducing activities of these analogues, suggesting a possible relationship between polymerase activation and interferon induction.

The ada gene of Escherichia coli K12, the regulatory gene for the adaptive response of bacteria to alkylating agents, was cloned in multicopy plasmids. O6-Methylguanine-DNA methyltransferase and 3-methyladenine-DNA glycosylase II, which are known to be inducible as part of the adaptive response, were produced in ada- cells bearing ada+ plasmids, even without treatment with alkylating agents. When such cells had been treated with methyl methanesulfonate, even higher levels of the enzyme activities were produced. Maxicell experiments revealed that the ada gene codes for a polypeptide with a molecular weight of 38 000. We constructed a hybrid plasmid carrying an ada'-lacZ' fused gene, with the proper control region for ada expression. beta-Galactosidase synthesis from the fused gene was strongly induced only when cells were treated with low doses of methylating agents, but was weakly induced with relatively high doses of ethylating agents. The induction was autogenously regulated by the ada gene product, in a positive manner.

Treatment of HeLa cells with interferon results in the induction of an enzymatic activity designated 2'5'oligo(A) polymerase. The polymerase requires continuous presence of double-stranded RNA (dsRNA) for activity, since degradation of dsRNA abolishes synthesis of the oligomeric series pppA(2'p5'A)n. These oligonucleotides are formed initially at a constant rate with dimer synthesized faster than trimer, and the latter faster than tetramer. After 45 min, accumulation of the dimer declines whereas that of other oligomers still proceeds at a linear rate. These results suggest that an oligomer remains associated with the enzyme for possible consecutive additions of adenylate, since no significant accumulation of dimer precedes synthesis of trimer. The relative amounts of the different oligomers found at the end of a reaction may reflect an increasing probability of release as the oligomers are elongated. The accumulation of dimer, however, decreases when it becomes a substrate for adenylate addition; incorporation of isolated dimer into 2'5'-oligo(A) was directly shown. Other nucleotides with a blocked p5'A terminus, like A5'ppppp5'A and NADH, can serve as adenylate acceptors in the presence of dsRNA. The adenosine triphosphates 2'-dATP and 3'-dATP are not incorporated efficiently into 2'5'-oligo(A) and inhibit its synthesis.

Escherichia coli B/r (suo) was infected, at 30 degrees C, with T4Dam+, T4DamB24-amN82 (I-, 44-, DNA-negative phenotype), and T4DamN134amBL292 (33-, 55-, maturation-defective phenotype). A genetic ('transformation') assay was used to monitor transcription of genes 30 (polynucleotide ligase), 42 (deoxycytidylate hydroxymethylase), 43 (DNA polymerase), rIIA, rIIB, and e (endolysin). The principal results are: (I) All of the genes studied were transcribed exlusively from the so-called l-strand of phage DNA. (2) DNA synthesis and the maturation-defective proteins were required to turn-off transcription of genes 42, rIIA, tIIB, and 43. Experiments performed with chloramphenicol suggested that all phage-specific proteins required to turn-off transcription of these genes were not present until 6 to 8 min post infection (p.i.). (3) During a normal developmental programme, gene 30 was transcribed throughout the eclipse. DNA-negative and maturation-defective conditions had no obvious effect on transcription of this gene. (4) During a normal lytic event, two discrete waves of gene e transcription were observed. The late wave was dependent upon DNA-synthesis and presence of functional maturation-defective proteins. The early wave was unaffected by DNA-negative or maturation-defective conditions. Experiments with chloramphenicol indicated that, if any virus-specific proteins are involved with regulation of early e transcription, such proteins are present by 3 min p.i. The data are interpreted to mean that early gene transcription is regulated by a minimum of two mechanisms. One of these mechanisms is fully operational by the 3rd min and, among the genes studied, controlled early e transcription. A second mechanism becomes operational between 6 and 8 min p.i. and controls transcription of genes 42, 43, rIIA, and rIIB.

The results presented above relate to several aspects of the 2-5A system. A simple but insensitive radiochemical assay fro 2-5A and its synthetase is described. Progress towards the molecular characterization of the synthetase suggested that it is composed of a single 56,000 dalton polypeptide chain that is synthesized in response to IF treatment. Degradation of 2-5A occurs at the same rapid rate in extracts of IF-treated and untreated chick cells. However, this breakdown can be inhibited by its end-product, 5'AMP, or by the activated synthetase which can further elongate 2-5A and thereby protect it from degradation. The direction of elongation is from the 5' to the 2' terminus. Molecules other than 2-5A can act as substrates fro 2'-adenylation by the activated synthetase. These include some dinucleoside monophosphates, ADP-ribose and NAD+, and methylene-bridged analogues of ATP. The methylene-bridged analogues of 2-5A that are synthesized in the latter case retain some of the biological activity of authentic 2-5A, indicating that cleavage of the 5'-terminal phosphate group(s) is not involved in the mechanism of nuclease activation by 2-5A.

Interferons induce an enzymatic activity that polymerizes ATP into 2'5'-oligoadenylate. This enzyme, designated 2'5'-oligo(A) polymerase, is induced in HeLa cells by type I interferon with a faster kinetics than by type II (immune) interferon. Cells treated with type I interferon in the presence of cycloheximide show elevated levels of polymerase when the inhibitor or protein synthesis is removed and actinomycin D is added to the cultures to prevent further synthesis of mRNA. This suggests that, in the presence of cycloheximide, interferon can activate transcription of mRNA for the 2'5'-oligo(A) polymerase, which is subsequently translated upon removal of this inhibitor. In contrast, cells treated with type II interferon in the same way do not show increased levels of polymerase. This indicates that type II interferon cannot activate transcription of a stable mRNA for the polymerase when protein synthesis is inhibited. This observation and the different kinetics of induction of 2'5'-oligo(A) polymerase suggest major differences in the mechanism of action of the different types of interferon, with type I being a "direct" inducer of the polymerase and type II an "indirect" inducer. The commitment of HeLa cells to the induction of 2'5'-oligo(A) polymerase declines if the cells are exposed to type I interferon in the presence of an inhibitor of RNA synthesis. This suggests that transcription of specific mRNAs is transiently activated by interferon and that repeated interaction of interferon with its receptor may be required for prolonged transcription of the mRNA for 2'5'-oligo(A) polymerase.

Interferon is part of the system of defence against viral infections and has important cell-regulatory and immunoregulatory functions. It is, however, not always possible to quantify circulating interferon in patients. An assay has been developed to measure an interferon-induced enzyme in white blood cells. The activity of this enzyme is constant in healthy subjects but increases by 2-10 times in 85% of patients with acute viral infections. It is also enhanced in autoimmune diseases and in virus-related malignancies and neurological disorders. The enzyme level was not raised in bacterial infections or non-infectious diseases studied. This simple and rapid biochemical assay of the interferon system could be used for diagnosis and evaluation of many diseases.

When bacteriophage lambda DNA replication is blocked by mutation in phage genes O or P, the efficiency of lysogenization drops to a very low value unless high multiplicities of infecting phage are used. Our results show that even at high multiplicity, lambda O or P mutants cannot efficiently lysogenize some hosts that are defective in either DNA polymerase I or DNA ligase. Covalent closure of infecting DNA molecules, a preliminary step for insertion according to Campbell's model and an obvious candidate for this lysogenization defect, appears to occur normally under our conditions. In addition, prophage excision as measured by the frequency of curing O- and P- lysogens seemed normal when tested in the poll- strain. These results suggest that the Escherichia coli enzymes DNA polymerase I and ligase, and phage proteins O and P, are able to provide some complementary activity whose function is required specifically for prophage integration.

The biosynthesis of early enzymes of DNA-ligase, RNA-ligase, DNA-polymerase, polynucleotide kinase, exonuclease A induced by bacteriophage T4amN82 was studied. The maximal activity of DNA-ligase was observed at the 60th min after the infection, while that of the other enzymes was revealed at the 90th min and reached 4, 45, 529, 120 and 78 units per mg of protein for DNA-ligase, RNA-ligase, polynucleotide kinase, DNA-polymerase and exonuclease A, respectively. Bacteriophage T4amN82 induced the maximal biosynthesis of the tested enzymes, when E. coli B-23 cells were grown in medium I containing trypton bacto ("Merck", West Germany) and a yeast extract ("Difco", USA). Similar events were observed when E. coli B-23 cells infected with phage T4amN82 were grown in a medium (II) with casein hydrolysate and yeast extract. Ultrasonication used for the disruption of E. coli B-23 cells infected with bacteriophage T4 had no effect on the enzyme activities.

We used alkA'-lacZ' and umuC'-lacZ' fused genes and determined the ability of various alkylating agents to induce adaptive and SOS responses. The degree of induction of expression of these genes was quantitatively measured by a simple colorimetric assay of beta-galactosidase activity. SN1 type methylating agents, such as N-methyl-N'-nitro-N-nitrosoguanidine and N-methyl-N-nitrosourea, were more effective inducers for the alkA than for the umuC system, while SN1 type ethylating agents, such as N-ethyl-N'-nitro-N-nitrosoguanidine and N-ethyl-N-nitrosourea, were more potent inducers for the umuC than for the alkA system. Similar but less striking effects on the two systems were obtained with SN2 type alkylating agents.

Genetic analyses of an Escherichia coli K-12 mutant possessing the amber mutation lig-321 were carried out. This mutant is defective in deoxyribonucleic acid (DNA) ligase and conditionally lethal. We constructed strains harboring an F'lig+ or F'lig-321 plasmid. Genetic complementation analyses were done by using these plasmids and by constructing a lig-4/F'lig-321 merodiploid. It was shown that lig-321 does not complement lig-4, unless the former is suppressed by an amber suppressor. The same was found to be the case between lig-321 and lig-ts7. Transductional mapping of lig-321, by a four-factor cross, revealed that lig-321 is very closely linked to lig-4. The frequency of recombinants between the two alleles was not unreasonable for assuming that they arose by intragenic recombination. The lig-4 and lig-ts7 alleles are known to reside in the structural gene for DNA ligase, in which lig-321 may also be located.

Treatment of a human monocyte-like cell line (U-937) by (2'-5')ApApA, the 5' dephosphorylated product of (2'-5')oligo-isoadenylate [oligo(A)] synthetase, an interferon-induced enzyme, was able to induce differentiation, mimicking the effect of interferon treatment. Treatment of U-937 cells with (2'-5')ApApA resulted in morphologic changes, new (monocyte-associated) membrane antigen expression, and acquisition of the capacity to mediate antibody-dependent cellular cytotoxicity (ADCC). (2'-5')ApA and (3'-5')ApApA were without effect. A myeloid cell line (HL-60) which differentiates in response to other agents, but not to alpha-interferon, was not able to differentiate in response to (2'-5')ApApA, despite the ability of interferon to induce (2'-5')oligo (A) synthetase.

A lambda vector that contains the gene for Escherichia coli DNA ligase (lambdagt4-lop-11 lig+) has been modified to achieve overproduction of this enzyme. The third Eco RI site in the lambda chromosome has been altered by mutation, and the left-hand Eco RI fragment has been shortened. The new vector, lambdagt4-lop-11 lig+, forms a stable lysogen which, upon induction, produces a 100-fold increase in DNA ligase activity. Introduction of a phage mutation (S7) that prevents cell lysis results in an even greater increase (500-fold).

After a nutritional shift from a protein-free to a diet containing 50% casein, the activity of DNA ligase increases in intact rat liver in correlation with the induction of hepatic DNA replication. The treated rat liver as well as control rat liver contains a single species of DNA ligase having a sedimentation coefficient of about 5.5 S. The administration of cycloheximide in vivo completely inhibits the increase in DNA ligase activity and in DNA synthesis, indicating that DNA ligase is induced in the hepatic cells replicating DNA. In contrast to DNA ligase, DNA kinase is unchanged in the activity level by the dietary manipulation.

The biological effects on diploid and trisomy 21 human fibroblasts of pure human interferon IFLrA, a single IFN-alpha species produced from cloned DNA, were compared with those of partially purified natural IFN-alpha. Twelve interferon-induced polypeptides were visualized by two-dimensional gel electrophoresis and autoradiography. Seven of these were shown to have related primary structures and are therefore products of related genes or are related through post-translational modification. Qualitative visual comparisons and computer-aided quantitation of autoradiograms revealed no differences in the patterns of polypeptide induction following treatment with the two types of IFN-alpha, and the two interferons also induced (2'-5') oligoisoadenylate synthetase equally. By these criteria, the activities of the two interferons are qualitatively and quantitatively indistinguishable. In addition, the effects of trisomy 21 on IFLrA-induced polypeptide synthesis and on antiviral response were similar to those previously demonstrated with natural IFN-alpha.

The cause of T7 exclusion by the F episome was investigated. Extracts from neither normal nor infected F+ cells contained an inhibitor of gene expression in vitro. The protein synthesizing systems prepared in vitro from these cells supported T7 early and late protein synthesis with normal efficiency. The content of translational initiation factors in F- and F+ cells, both noninfected and infected, was almost identical. The episome-dependent block of T7 gene expression was observed only in intact cells and detailed kinetics of gene expression in vivo revealed a stop of all transcription and translation at or just before 11 min after T7 infection. The mechanism of F+-dependent T7 exclusion involves both episomal and viral gene products. The data indicate that a T7-induced membrane alteration of the F+ cell membrane leads to cessation of T7 development as well as to the death of the host cell ('suicide').

The activity of 2',5'-oligoadenylate synthetase, which is induced by interferon action, was detected in mouse trigeminal ganglia infected with herpes simplex virus (HSV) type 1. When HSV was inoculated on the left cheek of mice, the virus began to appear in the ipsilateral trigeminal ganglia on day 2, reached its maximum accumulation on day 4, declined thereafter, and was no longer detected in the tissue homogenate after 11 days. After this short acute productive phase, the virus entered into the latent phase of infection. 2',5'-Oligoadenylate synthetase appeard in the trigeminal ganglia shortly after the beginning of virus multiplication; the synthetase activity began to rise on day 3, reached a maxium level on day 4, and then declined. Interferon activity (type I) also appeared in the infected ganglia, but diminished more rapidly than the synthetase. The antibody against HSV in the sera began to appear at the time when the virus and synthetase were declining. From these results it may be hypothesized, although not concluded, that in the acute productive phase of HSV infection in mouse trigeminal ganglia, virus multiplication is suppressed by interferon action, including 2',5'-oligoadenylate synthetase induction.

DNA ligase expression was studied in the embryonic chicken thymus. As previously reported, during thymus ontogeny two separate and successive (8S and 6S) forms of enzyme are found. The switch from the heavy to the light form takes place at around 18 days of incubation in situ. The demonstration that two successive generations of thymic lymphoid precursor cells develop in the embryonic bird thymus and that the replacement of the first by the second thymocyte generation takes place at around 18 days suggested the possibility that each form of enzyme could be restricted to a given thymocyte generation. By either culturing or transplanting embryonic thymuses of different ages it appears that the switch from the heavy to the light form of DNA ligase is not related to a change over of the first by the second generation of embryonic thymocytes but rather to some maturation process of the thymic lymphocytes starting from 17 days of embryonic life. The influence of extrathymic factors on the turning on of the expression of the 6 S DNA ligase in the post-natal environment is also suggested.

A further study of conditions for induction, determinations of activity and products of mRNAs translation of AVP having nonspecific antiviral activity from L-929 cells treated with poly(I) . poly(C) was carried out. Under conditions of superinduction of interferon the yield of AVP mRNA is reduced unlike that of interferon mRNA. Manifestations of the antiviral effect of AVP mRNA translation products do not seem to require the stages of transcription as dihydrorifampicin exerts no influence on this process. The inhibiting effect of actinomycin D is more likely to be associated with its effect on the energy of cells and synthesis of macroergic compounds of ATP type. Active AVP mRNAs from L-929 cells like interferon mRNA consist mainly of poly-A-deficient mRNAs. The sedimentation rate of AVP mRNAs differs from that of interferon mRNA and is about 10S. AVP mRNA translation products in ovocytes of Xenopus laevis, in contrast to control mRNAs, contain isoadenylate synthetase responsible for synthesis of 2'5'-oligoisoadenylate, a nonspecific translation inhibitor the mechanism of action of which consists in activation of cellular endogenous nuclease. The results suggest that the mode of development of the antiviral condition by activation of isoadenylate synthetase is similar in the cells treated with interferon and poly(I) . poly(C).

An enzymatic activity that synthesizes (2'-5')-oligo(A) from ATP is induced in animal cells treated with interferon. This activity, designated (2'-5')A polymerase, is also elevated in human lymphoblastoid Daudi and Raji cells treated with hydrocortisone. The polymerase activity increases significantly after 24 hr of treatment and declines when hydrocortisone is removed from the culture medium. The product of the enzyme prepared from hydrocortisone-treated cells is indistinguishable from (2'-5')oligo(A) synthesized with polymerase of interferon-treated cells either by an endonuclease activation assay or by chromatographic analysis. The increase in (2'-5')A polymerase is not mediated by secretion of interferon by hydrocortisone-treated cells; less than 1 unit of interferon per ml is present in the culture medium during treatment with this glucocorticoid hormone. Moreover, this increase is related to the concentration of hydrocortisone in the culture medium and is inhibited by the addition of cortexolone. This steroid interferes with the interaction between glucocorticoid hormones and their receptor. Cortexolone has no effect, however, on the induction of (2'-5')A polymerase by interferon. The synthetic glucocorticoid dexamethasone also increases the polymerase activity. Experiments with inhibitors show that such an increase requires RNA and protein synthesis.

Trisomy 21 human fibroblasts are more sensitive to human interferon-alpha (IFN-alpha) than are diploid controls, consistent with the location of the gene (IFRC) which codes for the IFN-alpha receptor on chromosome 21. When compared in the antiviral assay, the difference in sensitivity is five- to tenfold, much greater than the 50% difference in IFRC gene dosage. An understanding of the mechanism by which this amplification of gene dosage occurs is relevant to the specific pathology of Down's syndrome and as a model system for studying the pathogenic effects of chromosomal aneuploidy. The enzyme (2'-5') oligoisoadenylate synthetase (2-5A synthetase), which is believed to be central to the interferon-induced antiviral response, is induced 50% more in trisomy 21 fibroblasts than in diploid controls. Thus the amplification in response occurs subsequent to the binding of IFN-alpha to its receptor and the triggering of the first set of intracellular events, the latter exemplified by the induction of 2-5A synthetase. Similar results were obtained with IFN-gamma, consistent with other evidence which indicates that a gene coding for a separate IFN-gamma receptor is also located on chromosome 21.

A monospecific antibody against calf thymus DNA ligase composed of a single polypeptide with Mr = 130,000 cross-reacts with rodent and calf thymus DNA ligases. The antibody precipitates a single Mr = 200,000 polypeptide from detergent lysates of [3H] leucine-labeled mouse Ehrlich tumor cells and calf thymocytes. Pulse-chase experiments show that the Mr = 200,000 polypeptide in Ehrlich tumor cells has a half-life of about 0.5 h. In addition to the Mr = 200,000 polypeptide, a Mr = 130,000 polypeptide is detected in the partially purified enzyme preparations from radiolabeled Ehrlich tumor cells. These results suggest that DNA ligase is synthesized in mammalian cells as a Mr = 200,000 polypeptide and that the Mr = 200,000 polypeptide is degraded to a Mr = 130,000 polypeptide by a limited proteolysis in vitro.

The processing of the early T3 and T7 high-molecular-weight precursor messenger RNA by RNase III is necessary for its efficient translation both in vivo and in vitro.

Bacteriophage T7 bearing amber mutations in both gene 1.3 (T7 DNA ligase) and gene 3 (T7 endonuclease I) are viable when grown in suppressor-negative, ligase-negative hosts. This is evidenced by a high plating efficiency and a large burst size compared to the single mutants. These findings may be explained by a limited destruction of cellular DNA by the double mutant.