DNA polymerase activities in growing cells infected with simian virus 40

Construction and characterization of cDNA clones for four respiratory syncytial viral genes

Cytoplasmic poly(A)-containing RNA from respiratory syncytial virus-infected cells was used as a template to synthesize oligo(dT)-primed cDNAs. Discrete size classes of single-stranded cDNAs, resolved by alkali agarose gel electrophoresis, were used separately to construct double-stranded cDNAs that were subsequently inserted into the plasmid vector pBR322 at the Pst I site by means of oligo(dG)oligo(dC) tailing. After transfection of Escherichia coli, recombinant plasmids were screened mostly by serial rounds of hybrid selection of mRNAs from virus-infected cells and subsequent in vitro translation of the selected mRNAs. Comparative peptide mapping of the translation products with those of authentic virion proteins served to establish the viral origin of the cDNA recombinants. In this manner, four distinct classes of recombinant plasmids were identified. These encode sequences corresponding to those of respiratory syncytial virus nucleocapsid protein, matrix protein, phosphoprotein, and a nonstructural protein.

Increased activity of polynucleotide ligase in 5-iodo-2'-deoxyuridine and mitomycin C-pretreated simian virus 40 (SV40)-infected monkey kidney cells

The DNA ligase activity has been studied in 5-iodo-2'-deoxyuridine (IUdR), mitomycin C (MMC) and IUdR + MMC-treated SV40-infected or mock-infected CV1C11 monkey kidney cells. The results have shown that : 1. The level of enzyme activity is about two or three times higher in IUdR or MMC-treated non-infected cells; 2. SV40 infection doubles the level of ligase activity in the untreated cells; 3. There is an additional increase of ligase activity in IUdR or MMC-treated SV40-infected cells; 4. When infected or mock-infected cells are treated with IUdR + MMC, there is no modification of the results obtained with each drug alone; 5. Two peaks of different S values are detected in a partial purification of the drug(s) or viral induced enzyme(s). The increase in the ligase activity in drug-treated cells is independent of semi-conservative DNA synthesis. The drug(s) and viral-induced enzyme(s) is the consequence of a "de novo" synthesis of proteins, as shown by cycloheximide treatment.

Study of dogfish (Scyliorhinus caniculus) deoxyribonucleic acid polymerase alpha and beta. Extraction, separation, characterization and changes during spermatogenesis

DNA polymerase activity was extracted from testis cells of the dogfish Scyliorhinus caniculus. On a sucrose gradient, two main peaks could be separated, corresponding to DNA polymerases beta (3.8 S) and alpha (7.5 S). DNA polymerase gamma could also be detected when poly(A) . (dT)12 was used as template. The properties of alpha and beta polymerases of this primitive vertebrate were similar to those generally described, especially in mammals. The beta enzyme was highly sensitive to N-ethylmaleimide, however, and could use poly(dT) . poly(A) as template. Polymerase alpha was present in spermatogonia, spermatocytes and spermatids. Activity was maximal in spermatocytes. DNA polymerase beta was present in all testis cells with similar activities in spermatogonia and spermatocytes. Decreased activities were observed during spermiogenesis. Some activity remained associated with the chromatin fraction of mature sperm cells.

The influence of fluoro-phenyl-alanine on the synthesis of simian virus 40 DNA and T antigens

Treatment of Simian Virus 40 (SV40) infected monkey cells with fluorophenylalanine (FPA) resulted in increased uptake of thymidine by the cells, and progressive inhibition of both viral and cellular DNA synthesis. Viral DNA synthesis was more sensitive to inhibition by FPA than cell DNA synthesis. Synthesis of SV40 T antigens was however unaffected by FPA, as judged from immunofluorescence assays. The M.W. of the major polypetides immunoprecipitated from cell extracts by antibodies from tumor bearing hamster sera was similarly unaffected. It is suggested that T antigen synthesized in the presence of FPA is non functional.

DNA polymerase alpha, beta and gamma activities in ultraviolet irradiated CV-1 monkey cells

To determine the possible role of DNA polymerase alpha, beta and gamma during the repair period following ultraviolet (lambda max : 254 nm) irradiation of monkey CV-1 cells, we measured the three enzymatic activities by using specific tests, either in crude extracts or after fractionation by sucrose gradient (5--20%) centrifugation at high salt concentration. When compared to the unirradiated control, we could not detect any significant variation in the levels of activity of DNA polymerases alpha, beta and gamma at any time (0, 12 to 48 h) after ultraviolet irradiation of the cells with doses ranging from 9 to 52.5 J.m-2.

Utilization in vitro of deoxyuridine triphosphate in DNA synthesis by DNA polymerases alpha and beta from calf thymus

DNA polymerases alpha and beta (EC 2.7.7.7.) from calf thymus could utilize dUTP as a substrate for DNA synthesis as well as DNA polymerase I of Escherichia coli. Deoxyuridylate was incorporated into DNA by replacing deoxythymidylate and supported the further elongation of DNA chains on activated DNA or on the intiated homopolymers, poly(dA) . (dT)10 and poly(rA) . (dT)10. The rate of the incorporation of deoxyuridylate into DNA varied from 50 to 160% of that of deoxythymidylate, depending on the nature of the template primers and the species of DNA polymerase used. The apparent Km values for dUTP were very similar to those for dTTP. Uracil DNA-glycosylase excised efficiently the uracil residues in products of DNA polymerase reactions with either activated calf thymus DNA or initiated homopolymers.

Presence of two deoxyribonucleic acid polymerases in bull spermatozoa

A DNA polymerase-endogenous template complex was isolated from nuclear heads of bull spermatozoa. The buoyant density of the complex was 1.15 g/cm 3. The sedimentation coefficient of the nuclear DNA polymerase isolated from the complex was higher at low ionic strength, but approached 3.4S when centrifuged in a medium containing 2M-KCl. Activated exogenous DNA increased polymerase activity. Only very low activities were detected with synthetic templates such as poly(A).(dT)12-18 and poly(dT).poly(A). The nuclear reaction was stimulated by 150mM-KCl and was slightly inhibited by N-ethylmaleimide; it was resistant to actinomycin D, netropsin and ethidium bromide. Another DNA polymerase, highly sensitive to ethidium bromide, was extracted from the mitochondira-rich middle-piece fraction. Its sedimentation coefficient was close to 9S, but fell to approx. 4S in high-ionic-strength medium.

DNA polymerase alpha is associated with replicating SV40 nucleoprotein complexes

Simian virus 40 (SV40) nucleoprotein complexes were extracted from nuclei of infected monkey cells and fractionated on neutral sucrose density gradients. Complexes which contained replicating SV40 DNA (95S) separated well from those containing closed circular supercoiled viral DNA (75S). DNA polymerase activity was associated with the replicating nucleoprotein complexes but not with the slower sedimenting complexes. This DNA polymerase activity coprecipitated with the nucleoprotein complexes in the presence of MgCl2 and remained associated with the 95S complexes. This DNA polymerase activity has been identified as primarily DNA polymerase alpha on the basis of its sedimentation behavior, optimum salt concentration, and sensitivity to N-ethylmaleimide. DNA polymerase gamma activity was also detected in the complexes, but DNA polymerase beta was not associated with the complexes.

HeLa DNA polymerase alpha activity in vitro: specific stimulation by a non-enzymic protein factor

A non-enzymic protein factor that increases the in vitro rate of synthesis by HeLa DNA polymerase alpha 15- to 30-fold with denatured DNA as template has been partially purified from the cytoplasmic fraction of HeLa cells. The stimulatory effect is highly specific for HeLa DNA polymerase alpha and for DNA templates that contain extensive regions of single-strandedness. Synthesis with denatured DNA as template presumably proceeds from 3'-hydroxyl termini formed at loop-back regions since the synthesized DNA product and template are covalently linked. The stimulatory protein factor chromatographs as a basic protein, has an approximate molecular weight of 30,000 daltons and binds with moderate affinity to denatured DNA cellulose, being eluted by o.4M NaCl. The purified factor lacks detectable DNA polymerase, exo- and endodeoxyribonuclease and RNA polymerase activities. It also does not promote helix-coil transitions with poly[d(A-T)] and Clostridium perfringens DNA.