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Thrombin, a multifunctional serine protease, recognizes multiple macromolecular substrates and plays a key role in both procoagulant and anticoagulant functions. The substrate specificity of thrombin involves two electropositive surfaces, the fibrinogen-recognition and heparin-binding exosites. The SELEX process is a powerful combinatorial methodology for identifying high-affinity oligonucleotide ligands to any desired target. The SELEX process has been used to isolate single-stranded DNA ligands to human thrombin. Here, a 29-nucleotide single-stranded DNA ligand to human thrombin, designated 60-18[29], with a Kd of approximately 0.5 nM is described. DNA 60-18[29] inhibits thrombin-catalyzed fibrin clot formation in vitro. Previously described DNA ligands bind the fibrinogen-recognition exosite, while competition and photocrosslinking experiments indicate that the DNA ligand 60-18[29] binds the heparin-binding exosite. DNA 60-18[29] is a quadruplex/duplex with a 15-nucleotide "core" sequence that has striking similarity to previously described DNA ligands to thrombin, but binds with 20 to 50-fold higher affinity. The 15-nucleotide core sequence has eight highly conserved guanine residues and forms a G-quadruplex structure. A single nucleotide within the G-quadruplex structure can direct the DNA to a distinct epitope. Additional sequence information in the duplex regions of ligand 60-18[29] contribute to greater stability and affinity of binding to thrombin. A low-resolution model for the interaction of DNA 60-18[29] to human thrombin has been proposed.

Systematic Evolution of Ligands by EXponential enrichment (SELEX) was used to isolate from a population of 10(13) RNA molecules two classes of high affinity RNAs that bind specifically to human alpha-thrombin. Class I RNAs are represented by a 24-nucleotide RNA (RNA 16.24), and class II RNAs are represented by a 33-nucleotide RNA (RNA 27.33). RNA 16.24 inhibits thrombin-catalyzed fibrin clot formation in vitro. Secondary structures are proposed for these RNAs, revealing a novel stem-loop structure for RNA 16.24, comprised of an unusually large 16-nucleotide loop. Mutants of RNA 16.24 were generated to investigate structural features critical to high-affinity binding. Phosphate modification with ethylnitrosourea identified regions of the RNAs necessary for electrostatic interactions. Competition with heparin suggests that these RNAs bind the electropositive heparin-binding site of thrombin. These ligands represent a novel class of thrombin inhibitors that may be suitable for therapeutic or diagnostic applications.

Objective: Estrogen receptor-positive cancers that initially respond to hormone therapy often progress to a resistant state. The breast cancer cell line T47Dco is a model for such resistance. It is a polymorphic line, composed of multiple cell populations that demonstrate the presence of mutant estrogen receptors by cloning and sequencing techniques. Our objective was to isolate and analyze the structural and functional characteristics of the T47Dco mutant estrogen receptor complementary deoxyribonucleic acid clones., Study Design: We constructed two independent T47Dco complementary deoxyribonucleic acid libraries. We isolated and sequenced T47Dco estrogen receptors and have identified a mutant receptor that is truncated near the end of the deoxyribonucleic acid binding domain. This mutant has now been recreated with site-directed mutagenesis and tested for its ability to bind to deoxyribonucleic acid, dimerize with other estrogen receptors, and activate gene transcription by the chloramphenicol acetyltransferase assay and by gel shift assays., Results: The chloramphenicol acetyltransferase assays reveal that in the absence of estradiol low levels of conversion of chloramphenicol to acetylated products occur when the mutant estrogen receptor is used to activate chloramphenicol acetyltransferase gene transcription, supporting that it has some constitutive function. Also, gel mobility shift assays demonstrate low levels of deoxyribonucleic acid binding with the mutant protein., Conclusion: This mutant estrogen receptor may contribute to the estrogen receptor-positive, hormone-resistant phenotype of T47Dco cells by constitutively binding to and activating genes that were previously estradiol dependent.

The monoclonal antibody AB-52 has high affinity and specificity for the two natural human progesterone receptor forms, receptor A (hPRA) and receptor B (hPRB), but it does not bind the PR of chick, mice, rats or rabbits. We have used a novel method to map its epitope. Based on a series of site-directed mutants of hPRA, together with immunoblotting, DNA gel mobility shift and antibody super shift assays, we have mapped the epitope of AB-52 to a 17 amino acid sequence lying between Val221 and Leu237 of the 933 amino acid hPRB protein. This N-terminal sequence is common to both hPRB and hPRA but is missing in chick PR and differs extensively from mouse PR. No anti-rabbit PR antibodies map to the homologous rabbit PR sequence which differs from hPR by four amino acids, suggesting that one or more of these four amino acids form a critical subset of residues in hPR that define the human specificity of AB-52. Knowledge of the AB-52 epitope is useful in structural analysis of PR, and in competition studies. Additionally, this 17 amino acid peptide whose antigenicity would not be predicted from computer analysis, should be useful for generating additional hPR specific antibodies.

Antiserum prepared against homogeneous pig heart propionyl CoA carboxylase cross-reacted with human propionyl CoA carboxylase, and was used to demonstrate the presence of immunological cross-reacting material in extracts from the livers of three patients and from fibroblasts of four patients with propionic acidemia representing three major propionyl CoA carboxylase-deficient genetic complementation groups, pcc A, pcc C and bio. Since the quantity of cross-reacting material in the propionyl CoA carboxylase-deficient livers and enzyme-deficient fibroblast cell lines was comparable to that in normal tissues while showing less than five percent of the normal enzyme activity, these patients must synthesize normal or near-normal quantities of an enzymatically inactive propionyl CoA carboxylase protein. In addition, no appreciable change in the amount of cross-reacting material was found in the biotin-responsive bio fibroblasts after incubation with supplemental biotin despite a sixteen-fold increase in enzyme activity suggesting that the defect in the bio mutant involves the activation rather than the synthesis of a pre-existing normal apoenzyme.

Chromosome-specific DNA markers provide a powerful approach for studying complex problems in human genetics and offer an opportunity to begin understanding the human genome at the molecular level. The approach described here for isolating and characterizing DNA markers specific to human chromosome 15 involved construction of a partial chromosome-15 phage library from a human/Chinese hamster cell hybrid with a single human chromosome 15. Restriction fragments that identified unique- and low-copy loci on chromosome 15 were isolated from the phage inserts. These fragments were regionally mapped to the chromosome by three methods, including Southern analysis with a mapping panel of cell hybrids, in situ hybridization to metaphase chromosomes, and quantitative hybridization or dosage analysis. A total of 42 restriction fragments of unique- and low-copy sequences were identified in 14 phage. The majority of the fragments that have been characterized so far exhibited the hybridization pattern of a unique locus on chromosome 15. Regional mapping assigned these markers to specific locations on chromosome 15, including q24-25, q21-23, q13-14, q11-12, and q11. RFLP analysis revealed that several markers displayed polymorphisms at frequencies useful for genetic linkage analysis. The markers mapped to the proximal long arm of chromosome 15 are particularly valuable for the molecular analysis of Prader-Willi syndrome, which maps to this region. Polymorphic markers in this region may also be useful for definitively establishing linkage with one form of dyslexia. DNA probes in this chromosomal region should facilitate molecular structural analysis for elucidation of the nature of instability in this region, which is frequently associated with chromosomal aberrations.

The effects of ribose on the pre- and post-ischaemic functional performance of the isolated working heart from 24 month old chronically alcoholic animals was investigated. The improved perfusion model permitted the isolated heart to perform work analogous to that of the normal physiological load, in a system where systemic pressure and atrial pressure could be altered over a wide range and oxygen loss from the perfusion fluid was a minimum. There was a remarkable improvement in the performance of isolated hearts taken from alcoholic animals that were perfused with 1.7 mM ribose both before and after a 25.0 min period of global myocardial ischaemia (at 25 degrees C), however ribose treatment did not greatly affect the performance of hearts of isocaloric control aged rats. Chronic alcohol consumption significantly affected heart performance, causing a marked reduction in both cardiac and work output. After ischaemia the work of all hearts was notably decreased; there was no work output in untreated hearts of alcoholic animals, whereas in hearts of alcoholic animals treated with ribose work output was only decreased by 35%. The acute response to ribose by hearts of aged chronically alcoholic animals suggests a role for this compound as a positive inotropic agent and clearly indicates the beneficial potential of ribose for inclusion in cardioplegic solutions or for infusion in alcoholic subjects showing signs of heart failure or chronic heart disease.

Stimulation of transcription of reporter genes by the progesterone receptor (PR) was inhibited in transfected HeLa cells by co-expressing the estrogen receptor (ER) in an ER-dose- and estrogen-dependent manner. Both the N-terminal A/B region and the hormone binding domain of ER were involved in this inhibition, which was antagonized by antiestrogens and did not appear to involve direct interaction between ER and either reporter gene or PR. ER expression also inhibited activation by the glucocorticoid receptor (GR), and both PR and GR expression inhibited activation by ER, albeit to a lower extent. Similar transcriptional interference was observed between the endogenous PR and ER present in T47D and MCF-7 breast cancer cells transfected with an ER reporter gene. Moreover, transcription of the resident estrogen-induced pS2 gene was partially inhibited by exposing MCF-7 cells to progestins or glucocorticoids. We propose that these observations reflect competition for a functionally limiting transcription factor(s).

We have previously reported the presence of a hormone-inducible transcriptional activation function (TAF-2) within the region of the estrogen receptor (ER) that contains the hormone binding domain. We show here that the N-terminal A/B region of the ER contains an independent constitutive activation function (TAF-1) that exhibits cell type specificity since it activates transcription efficiently in chicken embryo fibroblasts, but only poorly in HeLa cells. By analyzing the ability of TAF-1, TAF-2, and the GAL4 and VP16 acidic activating domains (AADs) to homosynergize and heterosynergize with one another and with the factor binding to the upstream element (UE) of the adenovirus 2 major late promoter, we show that the activation properties of TAF-1 and TAF-2 are different and distinct from those of AADs, in agreement with the absence of acidic amino acid stretches in TAF-1 and TAF-2.