Effects of Polyribonucleotides of Known Composition on Deoxycytidylate and Deoxyguanylate Kinase Activity in Pneumococci

Characterization of a multienzyme complex derived from a Bacillus subtilis DNA-membrane extract that synthesizes RNA and DNA precursors

The activity of a variety of enzymes involved in the synthesis of RNA and DNA precursors was found to copurify with initiation of DNA replication activity. These enzymes included ribo- and deoxyribonucleoside kinases, kinases for their phosphorylated intermediates, and ribonucleoside diphosphate reductase. This precursor-synthesizing complex is part of a Bacillus subtilis DNA-membrane extract originally shown to contain all of the enzymes and template necessary for initiation of DNA replication (J. Laffan and W. Firshein, J. Bacteriol. 169:2819-2827, 1987). Although the complex incorporated deoxyribonucleoside triphosphates into DNA, deoxyribonucleosides were incorporated even faster, suggesting catalytic facilitation. Both ribonucleosides and deoxyribonucleosides were found by thin-layer chromatography separation to be converted by the complex into their mono-, di-, and triphosphate derivatives. Ribonucleotides were incorporated into DNA via the action of ribonucleoside diphosphate reductase. Some regulatory mechanisms of the kinase system may also be retained by the complex. Electron microscope studies revealed that the precursor-synthesizing-initiation subcomplex is contained within a particulate fraction consisting of different-size vesicles resembling liposomes and that these particles may be structurally important in maintaining the synthetic activity of the subcomplex.

Enrichment of DNA polymerase III activity in a DNA membrane complex purified from Pneumococcus: the possible existence of subcomplexes

Three DNA polymerase activities, one related to DNA pol III, have been extracted from a DNA membrane complex purified from Streptococcus pneumoniae. DNA pol III was purified 3300-fold, DNA pol II 2800-fold and DNA pol I 1800-fold. Based on inhibition analysis with a drug known to inhibit DNA pol III activity in Gram positive organisms. 6(p-hydroxyphenyl azo) uracil (HpU), 55% of the total DNA polymerase activity is represented by pol III. In contrast, only 3-5% of the total DNA polymerase activity is inhibited by HpU in crude extracts. The purification of the DNA membrane complex from pneumococcus is modified from an earlier procedure (Firshein 1972). The modified procedure results in the separation of three distinct DNA-protein-phospholipid subcomplexes of which the one described above contains most of the radioactivity derived from cells pulsed for a short time with (3H)-thymidine. Proteins are involved in binding DNA in each complex and the conformation of DNA in each complex may be different. All of the subcomplexes contain DNA polymerase activity partially sensitive to HpU. These results provide direct evidence for the structural integrity of a complex that may be involved in DNA replication in vivo.

Two membrane sites for DNA synthesis in Pneumococcus

A DNA membrane fraction extracted from pneumococci can be separated into two subfractions with respect to macromolecular composition and DNA synthesis by centrifugation in a 30-60% w/v neutral sucrose gradient. Each fraction can be rebanded in a sucrose gradient or centrifuged to equilibrium in a CsCl density gradient without altering the ability of the fractions to synthesize DNA. The fast sedimenting (heavy) fraction contains 45% of the DNA, and the bulk of the phospholipid, protein, and RNA. The light fraction contains 50% of the DNA, and lower, but significant amounts of phospholipid, RNA, and protein. Both fractions contain a DNA replication complex consisting of a number of enzymes involved in synthesizing DNA or DNA precursors, as well as RNA polymerase activity. However, the specific activity of DNA polymerase in the light fraction is much greater than that in the heavy fraction. In addition, the following results suggest that the former is concerned primarily with replication of the genome while the latter has characteristics of a repair function for the genome. (1) newly synthesized DNA can be detected within 30 s in the light fraction but not until 4 min in the heavy fraction. (2) an RNA-DNA single-stranded hybrid can be demonstrated during initial stages of DNA synthesis in the light, but not heavy fraction. (3) extensive semiconservative DNA replication occurs in the light fraction, whereas little such replication is detected in the heavy fraction. (4) DNA polymerase activity in the light fraction has several of the characteristics of a polymerase identified by others as being concerned with normal DNA replication, such as inhibition by N-ethylmaleimide, and relatively high rates of chain elongation (4.9 x 10(4) nucleotides/min). In contrast, DNA polymerase activity in the heavy fraction has characteristic properties associated with DNA polymerase I, a possible repair enzyme. These include higher activity for a d(A-T)n template than that detected in the light fraction, no effect of N-ethylmaleimide, and relatively low rates of chain elongation (9 x 10(3) nucleotides/min).

Role of polyadenylic acid in a deoxyribonucleic acid-membrane fraction extracted from pneumococci

After the addition of radioactive polyadenylic acid to cell suspensions of pneumocci, part of the radioactivity becomes associated with a deoxyribonucleic acid (DNA)-membrane fraction extracted from the cells. A variety of techniques show that a portion of this associated radioactivity may represent oligoadenylates complexed to DNA, probaby as part of a ribonucleic acid (RNA) component. Polyadenylic acid, which had previously been shown to enhance DNA synthesis in cell suspensions (Firshein and Benson, 1968), also enhances the extent of DNA synthesis by the DNA-membrane fraction in vitro under specific conditions of concentration and conformation. The mechanism of action of this enhancement may be related to the ability of oligoadenylates to increase the number of initiation sites for DNA replication by stimulating the production of an RNA primer, thus providing additional 3'-OH groups with which DNA polymerase can react.

Role of deoxyribonucleic acid ligase in a doxyribonucleic acid membrane fraction extracted from pneumococci

Deoxyribonucleic acid (DNA) ligase has been detected in a DNA membrane fraction extracted from Pneumococcus. The specific activity of the enzyme in this fraction is 10-fold greater than in the remaining cell extract. It remains firmly bound (with other enzymes) to the complex after a purification procedure in which a considerable percentage of the macromolecules are dissociated. The ligase acts in two ways in the DNA membrane fraction in vitro. One, it catalyzes the linkage of small-molecular-weight pieces of newly synthesized DNA into heavier-molecular-weight DNA strands as shown by others (M Gellert, 1976; R. Okazaki, A. Sugino, S. Hirose, T. Okazaki, Y. Imae, R. Kainuma-Kuroda, T. Ogawa, M. Arisawa, and Y. Kurosowa, 1973; B. Olivera and I. Lehman, 14; and A. Sugino, S. Hirose, and R. Okazaki, 1972) and, two, it protects DNA from degradation by deoxyribonucleases. This latter effect is due to a competition between the ability of the nucleases to degrade DNA and the ability of DNA ligase to seal the nicks produced by these degradative enzymes. The ligase acts cooperatively with other enzymes in the DNA membrane fraction to synthesize DNA.

In situ activity of enzymes on polyacrylamide gels of a deoxyribonucleic acid-membrane fraction extracted from pneumococci

A deoxyribonucleic acid (DNA)-membrane fraction extracted from Diplococcus pneumoniae was subjected to polyacrylamide gel electrophoresis after treatment with 0.16% sodium dodecyl sulfate. At least two DNA polymerase activities were detected by in situ assays with appropriate substrates, templates, and inhibitors, including a co-polymer of deoxyadenylic and thymidylic acid and N-ethylmaleimide. This activity coincided with a fraction in the gel containing 7.5, 9.4, and 24%, respectively of the DNA, phospholipid, and protein present in the DNA-membrane fraction before electrophoresis and sodium dodecyl sulfate treatment. Assays with minced gels showed that several nuclease activities, deoxyribonucleotide kinase activity, and DNA ligase activity also coincided with this fraction. However, ribonucleoside diphosphate reductase activity did not. These results demonstrate that a complex of enzymes involved in DNA replication is firmly bound to the DNA-membrane fraction in pneumococci.

Release of nuclear DNA template restrictions by specific polyribonucleotides

Certain synthetic homo- and copolyribonucleotide polymers are capable of releasing the DNA template restriction of isolated nuclei of rat liver cells when assayed with an excess of or in the absence of exogenous DNA polymerase. The purine homopolyribonucleotides are far more effective than are the pyrimidine polymers.

DNA-membrane complex: macromolecular content and stimulation of enzymatic activity by polyadenylic acid

A DNA-cell membrane complex has been isolated from cell suspensions of virulent pneumococci by sarcosyl lysis followed by centrifugation on a sucrose gradient. When polyadenylic acid plus the eight naturally occurring deoxyribonucleosides and deoxyribonucleotides are added to cell suspensions, the percentage of total DNA in the complex increases with incubation time. This increase is not observed in unsupplemented cell suspensions. However, the percentages of RNA, protein, and phospholipid do not increase with incubation time in either supplemented or control complexes. A variety of deoxyribonucleotide kinases and the DNA polymerase are also detected in the DNA-membrane complex, and their specific activities are greater in complexes extracted from supplemented cell suspensions than in those extracted from controls.

Characterization of excess deoxyribonucleic acid synthesized by pneumococci in the presence of polyadenylic acid and deoxyribonucleic acid precursors

Excess deoxyribonucleic acid (DNA) synthesized by cell suspensions of encapsulated pneumococci in the presence of polyadenylic acid plus all eight of the naturally occurring deoxyribonucleosides and deoxyribonucleotides has been characterized in several ways. The DNA represents complete molecules, is synthesized by a relatively large population at a steady rate, and is replicated in a semiconservative manner.

Tyrosine aminotransferase: enzyme induction independent of adenosine 3', 5'-monophosphate

The importance of adenyl cyclase and adenosine 3',5'-monophosphate in the induction of tyrosine aminotransferase by adrenocorticosteroids has been tested in HTC cells derived from a rat hepatoma and grown in tissue culture. Adrenocorticosteroids cause a 10-to 15-fold increase in the rate of synthesis of tyrosine aminotransferase in these cells. Under various experimental conditions, with or without glucocorticoids, neither adenyl cyclase nor cyclic adenosine mono-phosphate could be detected in HTC cells. In addition, neither the cyclic nucleotide nor N(6), O(2')-dibutyryl cyclic adenosine monophosphate caused increased activity of the transaminase in HTC cells. We conclude that induction of tyrosine aminotransferase by glucocorticoids is not mediated by the adenyl cyclase-cyclic adenosine monophosphate system.