DNA polymerase I from Acinetobacter calcoaceticus: enzymatic properties

Properties of a DNA repair endonuclease from mouse plasmacytoma cells

The properties of a DNA-repair endonuclease isolated from mouse plasmacytoma cells have been further studied. It acted on ultraviolet-light-irradiated supercoiled DNA, and the requirement for a supercoiled substrate was absolute at ultraviolet light doses below 1.5 kJ m-2. At higher doses relaxed DNA could also serve as a substrate, but the activity on this DNA was due mostly to hydrolysis of ultraviolet-light-induced apurinic/apyrimidinic (AP) sites by the AP-endonuclease activity associated with the enzyme. The latter enzyme activity did not require a supercoiled form of the DNA. The enzyme also introduced nicks in unirradiated d(A-T)n. The nicked ultraviolet-light-irradiated DNA served as a substrate for DNA polymerase I, showing that the nicks contained free 3'-OH ends. Treatment of the nicked ultraviolet-light-irradiated DNA with bacterial alkaline phosphatase followed by T4 polynucleotide kinase, resulted in the phosphorylation of the 5' ends of the nicks, indicating that the nicks possessed a 5'-phosphate group; 5'- and 3'-mononucleotide analyses of the labelled DNA suggested that the enzyme introduced breaks primarily between G and T residues. The enzyme did not act on any specific region on the supercoiled DNA molecule; it produced random nicks in ultraviolet-light-modified phi X 174 replicative form I DNA. Antibodies raised against ultraviolet-light-irradiated DNA inhibited the activity. DNA adducts such as N-acetoxy-2-acetylaminofluorene and psoralen were not recognized by the enzyme. It is suggested that the enzyme has a specificity directed toward helical distortions.

DNA polymerase of a basidiomycete fungus, Coprinus cinereus

DNA polymerase activity was studied in Coprinus cinereus, a basidiomycete fungus. Only one from of the enzyme could be demonstrated, whether by affinity or ion-exchange chromatography; this enzyme had a molecular weight of 185000 on Sephadex G-200, and was inhibited by mercaptoethanol. Coprinus, a representative of the most advanced type of the filamentous fungi, resembles other eukaryotic micro-organisms in its lack of a mammalian beta-type DNA polymerase. The properties of the polymerase are compared with those of two other fungi, and found to resemble most closely the yeast polymerase A in Mg2+ requirements and template preference.

DNA-RNA polymerase complexes associated with the membrane from bacteriophage T2- or T4-infected Escherichia coli. I. General properties

Properties of DNA-RNA polymerase complexes, apparently bound to a fraction of the cell membrane of bacteriophage T2- or T4-infected Escherichia coli, are described. Evidence is presented to show that the complexes initiate the asymmetric synthesis of RNA, and release the finished product. The transcription capacity per unit of beta' + beta was 10 times higher at 6 min than at 30 min after infection.

Preparations and properties of ribonucleic acid polymerase from Acinetobacter calcoaceticus

Deoxyribonucleic acid (DNA)-dependent ribonucleic acid (RNA) polymerase (EC 2.7.7.6) from Acinetobacter calcoaceticus was purified to apparent homogeneity and its properties were compared with those of the Escherichia coli B enzyme. The molecular weights of the two native active enzymes as well as their alpha and beta subunits appeared to be similar. No subunit corresponding to that of sigma from E. coli was found, and furthermore no separation between the beta subunits could be detected by gel electrophoresis. A number of different DNAs were transcribed by the enzyme from A. calcoaceticus. Maximal RNA synthesis occurred at pH 8.7, 10 mM Mg2+, or 0.3 mM Mn2+ and at a total ionic strength of 0.1. Higher ionic strengths led to increasing inhibition of transcription and at mu = 0.4 complete inhibition was observed. The mechanism of inhibition of salt was not related to the initiation event as observed with T4 core RNA polymerase (R.Kleppe, 1975). In an attempt to understand the mechanism of inhibition by salt, the effect of ionic strength on the sedimentation properties of the enzyme was investigated. At low ionic strength, enzyme species with sedimentation coefficients, s20,w, of 5.8S, 12.4S, and 19.3S were present. In buffers with higher ionic strengths the relative amounts of the 12.4S species decreased. It is suggested, therefore, that the inhibition of activity at higher salt concentrations is caused by a decrease in concentration of the active enzyme species.

Preparation and separation of d(pT)-10-n oligonucleotides

A series of oligomers having the general formula d(pT)-10-n, n varying from 2 to 20, has been prepared by enzymatic joining of d(pT)-10, annealed on poly dA, employing T-4 polynucleotide ligase. The oligomers could be separated on 8 or 12% polyacrylamide gels. Such oligomers may prove useful as molecular weight markers and initiators for various polymerases.