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A Hizi

Publications and source records attributed to A Hizi.

85 records · Page 5Linked to original sources
PubMed1980

RNA-dependent DNA polymerase of an endogenous type C virus of mice: purification and partial characterization.

An RNA-dependent DNA polymerase was isolated from purified virions of endogenous oncornaviruses released by the MOPC-315 murine myeloma cell line. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the purified enzyme was found to consist of two major polypeptides with molecular weights of about 28,000 and 26,500. The active enzyme had a molecular weight of approximately 56,000, as calculated from its sedimentation on glycerol density gradients, indicating that it is probably a dimer of the two subunit polypeptides. The isolated MOPC-315 virus polymerase exhibited all three activities known to be found in the DNA polymerase from oncornaviruses, namely, an RNA-dependent DNA polymerase, a DNA-dependent DNA polymerase, and an RNase H. The RNA-dependent polymerase activity showed a prounced preference for Mn2+ over Mg2+, whereas the DNA-dependent and RNase H reactions were catalyzed by these two cations to an almost equal extent. The purified polymerase was found to be immunologically related to the polymerase of Rauscher murine leukemia virus.

Animals↗
PubMed1978

Prolactin synthesis by human chorion-decidual tissue: a possible source of prolactin in the amniotic fluid.

Explants of human chorion-decidual tissue obtained at delivery from normal, full-term pregnancies synthesize and secrete prolactin. This hormone is indistinguishable from pituitary prolactin by chromatographic, electrophoretic, immunologic, and receptor assay techniques. These results suggest that chorion-decidua may be the source of the large quantities of prolactin in amniotic fluid.

Amnion↗
PubMed1977

The RNA-dependent DNA polymerase of avian sarcoma virus B77. Binding of viral and nonviral ribonucleic acids to the alpha, beta2, and alphabeta forms of the enzyme.

The extent of binding of various RNA species to the three forms of avian sarcoma virus B77 RNA-dependent DNA polymerase was determined using a sensitive nitrocellulose filter binding technique which was capable of detecting binding reactions with association constants as low as 3 X 10(6) liters X mole-1. All three enzyme forms, alphabeta, beta2, and alpha, bound to all single-stranded RNA species that were tested, including nonviral RNAs. 70 S viral RNA exhibited the highest association constant (about 10(11) liters X mole-1), and a population of virus-derived tRNA molecules from which tRNATrp had been removed, the lowest (about 3000 times lower). The affinity for other RNAs was roughly proportional to their size. The affinity of RNAs for the alphabeta enzyme form always exceeded that for the two others by a factor that depended on the particular RNA, never exceeded 6 and was sometimes as low as 1.2. The association constant of the alphabeta enzyme form with viral 70 S RNA was about 15-fold higher than that with viral 35 S RNA. 35 S RNA annealed to tRNATrp had an association constant that was only 2.5 times higher than that of 35 S RNA alone. This finding suggests that the tertiary structure of 70 S RNA plays a significant role in its affinity for B77 DNA polymerase.

Avian Sarcoma Viruses↗
PubMed1977

RNA-dependent DNA polymerase of avian sarcoma virus B77. I. Isolation and partial characterization of the alpha, beta2, and alphabeta forms of the enzyme.

Three forms of the RNA-dependent DNA polymerase were isolated from highly purified avian sarcoma virus B77 grown in duck embryo fibroblasts, using sequential chromatography on DEAE-cellulose, phosphocellulose, and poly(U)-cellulose. One form, which sedimented with about 5.2 S, contained only one species of polypeptide, with a molecular weight of 63,000; a second sedimented with about 7.8 S and contained only one species of polypeptide with a molecular weight of 81,000; and a third form, which sedimented with about 7.3 S, contained two species of polypeptides with molecular weights of 63,000 and 81,000. The molecular constitution of the three enzyme forms were therefore alpha, beta2, and alphabeta. All three possessed almost the same specific activity with poly(rA)-oligo(dT) as the primer-template. Forms alpha and alphabeta of avian sarcoma virus DNA polymerase have already been described in the literature; form beta2 is a new form. All three forms possessed ribonuclease H activity, the relative specific activities of the alpha, beta2, and alphabeta forms being about 1:4:5. All three enzyme forms were inhibited by antiserum to the alphabeta form, but whereas the alpha and alphabeta forms could be inhibited about 95%, the maximum degree of inhibition of the beta2 form was about 80%. The three enzyme forms also differed with respect to heat stability at 46 degrees, the monomeric alpha form of the enzyme being only about one-half as stable as the two dimeric forms.

Avian Sarcoma Viruses↗
PubMed1977

RNA-dependent DNA polymerase of avian sarcoma virus B77. II. Comparison of the catalytic properties of the alpha, beta2, and alphabeta enzyme forms.

The alpha, beta2, and alphabeta forms of the RNA-dependent DNA polymerase of avian sarcoma virus B77 grown in duck embryo fibroblasts have been compared with respect to several kinetic properties. The following results were obtained. 1. The Km values for dTTP and dGTP for enzyme forms alpha, beta2, and alphabeta were 77, 39, and 74, and 6.8, 3.1, and 6.1 micronM, respectively. 2. The affinity of 70 S Rous sarcoma virus RNA for enzyme form alphabeta was about twice that for the other two forms. 3. The relative specific activities of the three enzyme forms on synthetic primer-templates such as poly(rA)-poly(dT) were almost the same. The viral 70 S RNA-dependent specific activities were 2 to 3 orders of magnitude lower and in the ratio of 1:3:5 for enzyme forms alpha:beta2:alphabeta. Addition of exogenous oligo(dT) stimulated the 70 S viral RNA-dependent activity of enzyme forms alphabeta and beta2 by a factor of 3, and that of enzyme form alpha by a factor of 30, so that it then became the most active transcriptase of viral 70 S RNA. 4. The largest transcripts formed by the three enzyme forms with 70 S viral RNA as primer-template were about 4,500 nucleotides long. About one-third of the total amount of polynucleotides polymerized by the alphabeta enzyme was in the form of such transcripts. This proportion was far higher than for the other two enzyme forms. 5. All three enzyme forms were capable of transcribing single-stranded into double-stranded DNA. 6. The 3-propylcyclohexyl piperidyl derivative of rifamycin SV, at a concentration of 100 microng/ml, inhibited enzyme forms beta2 and alphabeta by over 99.5 and 96%, respectively, but enzyme form alpha by only about 60%. 7. The beta2 and alphabeta forms of the enzyme were processive DNA polymerases, the alpha form a nonprocessive polymerase. 8. In general, these results indicate that in most respects the properties of the dimeric enzyme forms resemble each other much more closely than those of the alpha form. In some very important respects, such as affinity for viral RNA and the size of transcripts formed from it, the alphabeta enzyme form performs significantly better than either of the other two enzyme forms.

Avian Sarcoma Viruses↗