Low molecular weight DNA polymerase of rat ascites hepatoma cells

Purification and characterization of a beta-like DNA polymerase from Trypanosoma cruzi

A DNA polymerase was purified to near homogeneity from Trypanosoma cruzi epimastigotes. This preparation had a major polypeptide of 50 kDa and a minor band of 45 kDa. SDS-PAGE studies and a novel colorimetric activity gel technique demonstrated that the 50-kDa polypeptide chain is the catalytic subunit of this T. cruzi DNA polymerase. Western blot analysis of different purification stage fractions strongly suggests that this 50-kDa protein is the intact catalytic subunit and does not correspond to a degradation product from a larger one. This T. cruzi DNA polymerase is insensitive to aphidicolin, butylphenyldeoxyguanosine triphosphate, berenil, ethidium bromide and N-ethylmaleimide, but is markedly inhibited by the dideoxythymidine triphosphate analogue. Studies with different DNA templates showed that the DNA polymerase prefers activated DNA as substrate and that it cannot elongate oligoriboadenylate primers. The data presented in this paper are consistent with the hypothesis that this enzyme corresponds to a beta-like DNA polymerase present in the parasitic protozoon T. cruzi.

DNA polymerases of rat liver. Partial characterization and effect of various inhibitors

Three distinct DNA-dependent DNA polymerase activities have been partially purified from normal rat liver. Soluble activities are separable into two distinct fractions (P1 and P2) by phosphocellulose chromatography. A low-molecular-weight DNA polymerase was isolated from purified nuclei. The enzymes were characterized according to chromatographic and sedimentation behavior, enzymological properties, and response to various inhibitors. The results indicate that fraction P1 corresponds to the high-molecular-weight enzyme and suggest that polymerase P2 may be derived from partial dissociation of the high-molecular-weight enzyme. The molecular weight of polymerase P1 was estimated to be about 250 000 by Sephadex column chromatography. Both fraction P2 and nuclear DNA polymerase appeared to be low-molecular-weight enzymes. However, the molecular size of these activities was apparently different. The estimated molecular weights of nuclear and P2 enzyme are about 40 000 and 25 000, respectively. As with the nuclear enzyme, polymerase P2 (but not P1) appeared to be free of detectable exonuclease activity. All of these polymerases showed a marked preference for initiated polydeoxyribonucleotide templates. The rat liver polymerases differed in their ability to use poly[d(A-T)-A1 primer-template, as is shown by the ratios of their activity with this synthetic polymer to that with activated DNA: 0.5, 2.75, and 1.34 for P1, P2, and nuclear polymerase, respectively. Denatured DNA was a poor template for both enzymes P1 and P2, but it was inert as template for the nuclear enzyme. Although each of these polymerases required all four deoxynucleoside triphosphates for maximal activity, they catalyzed a high rate of synthesis in the absence of one or more deoxynucleoside triphosphates. Such a 'limited' synthesis was much more extensive for polymerase P2 and nuclear enzyme than for P1 was the most sensitive of the three to sulphydryl reagents, ehtidium bromide, heparin, and single-stranded DNA. The responses of P2 and nuclear enzymes to various inhibitors were very similar. However, these two enzymes respond differently to heat and high ionic strength.

Differentiation and characterization of the cytoplasmic and nuclear deoxyribonucleic acid polymerases from baby hamster kidney cells

Distinct DNA polymerase activities have been found in the cytoplasmic and nuclear fractions of a baby hamster kidney cell line. They were separated by chromatography on DEAE-cellulose and partially purified by ammonium sulfate fractionation, DNA - cellulose and linear sucrose gradients. The cytoplasmic DNA polymerase exhibited an S-coefficient of 6.95 S in 0.15 M NaCl and its activity was highly sensitive to inhibition by N-ethylmaleimide and elevated temperatures, regardless of the presence of DNA template or other cofactors. It was stimulated by monovalent salts in the order of NH4 Cl greater than KCl greater than NaCl greater than CsCl greater than LiCl (inhibitory). The DNA polymerase extracted from nuclei sedimented with an S-value of 3.47 S, was resistant to inactivation by N-ethylmaleimide, and maximally stimulated by NaCl, while also being inhibited by LiCl. For optimal activity, both DNA polymerase activities required a divalent cation, with MgCl2 being more effective than MnCl2. Although the optimal pH values for the two enzyme activities differed slightly, glycine - NaOH buffer induced an alkaline shift of 1.5 pH units in the optimum of both enzymes. This was accompanied by an increase in the effectiveness of MnCl2 relative to MgCl2 for the cytoplasmic DNA polymerase.