Studies on the molecular species of DNA polymerase extracted from rat ascites hepatoma cells

Effects of aging and dietary restriction on DNA polymerases: gene expression, enzyme fidelity, and DNA excision repair

Hepatic DNA polymerases isolated from young and old C57BL/6N mice fed ad libitum or calorically restricted differed in chromatographic characteristics, binding affinity for DNA template-primer, specific activity, and fidelity of synthesis. DNA polymerase alpha total and specific activity declined slightly, while the nucleotide misincorporation frequency increased dramatically, with increased age of the donor animals. A positive correlation was observed between polymerase alpha specific activity and the affinity of enzyme binding to activated DNA template-primer. Both the age-associated decline in enzyme activity and the decrease in fidelity of synthesis were modified by dietary restriction, with higher specific activity levels and lower misincorporation frequencies for DNA polymerases from dietarily restricted animals compared with ad libitum animals of all ages. Fidelity of both DNA polymerase alpha and beta increased following treatment with the phosphoinositide hydrolysis product inositol-1,4-bisphosphate. The data suggest that dietary restriction could play an important role in decreasing the age-associated decline in function of physiological systems sensitive to decreased or defective DNA synthesis.

Effects of aging and dietary restriction on DNA polymerase expression in mice

DNA polymerase alpha was isolated from livers of 6-month-, 16-month-, or 26-month-old mice fed ad libitum, or calorically restricted. The enzymes differed in chromatographic characteristics, binding affinity for DNA, and activity, with both total activity and specific activity of DNA polymerase alpha decreasing as a function of age. A positive correlation was observed between polymerase alpha specific activity and the affinity of enzyme binding to activated DNA template-primer. The age-associated decline in enzyme activity was modified by dietary restriction, with measurably higher activity seen for polymerases from dietary restricted animals compared with ad libitum animals of all ages. The data suggest that dietary restriction could act to delay the age-associated decrease in cellular capacity for DNA synthesis, which may play a significant role in prolonging the onset of age-related diseases in which decreased DNA synthesis is a potential component.

Size difference in catalytic polypeptides of two active forms of mouse DNA polymerase alpha and separation of the primase subunit from one form, DNA replicase

There are two active forms of DNA polymerase alpha in mouse cells. One form (DNA replicase) is a DNA polymerase associated with primase activity and the other form (7.3 S polymerase) has no primase activity (Yaugar, T., Kozu, T. and Seno, T. (1982) J. Biol. Chem. 257, 11121-11127). The primase activity was dissociated from partially purified DNA replicase by hydroxyapatite column chromatography in buffer containing dimethyl sulfoxide and ethylene glycol. Nearly homogeneous primase, consisting of a 58 kDa polypeptide was obtained by glycerol gradient sedimentation and DEAE-cellulose column chromatography. Experiments on the effect of proteinase treatment and measurement of the molecular weight of the catalytic polypeptide of DNA replicase after its dissociation from the primase polypeptide indicated that the primase is not part of the DNA polymerase molecule, but an independent protein associated with DNA polymerase alpha, and that the latter is a 115 kDa catalytic polypeptide. The other form of DNA polymerase alpha, 7.3 S polymerase, consists of a 72 kDa catalytic polypeptide. Thus, the two forms of mouse DNA polymerase alpha have partially, if not completely, different catalytic polypeptide structures, suggesting that the 7.3 S polymerase is not simply formed from DNA replicase by dissociation of the primase subunit.

Large polypeptides of 10S DNA polymerase alpha from calf thymus: rapid isolation using monoclonal antibody and tryptic peptide mapping analysis

The polypeptides recognized by a monoclonal antibody against calf thymus DNA polymerase alpha (secreted from a hybridoma CL22 -2- 42B , Nucleic Acids Res. (1982) 10, 4703-4713) were identified by the immunoblot method as the large polypeptides of the partially-purified 10S DNA polymerase alpha fraction. Using an immunoprecipitation technique with the monoclonal antibody, a rapid immunological isolation of the polypeptides has been achieved. By this method, the large polypeptides with Mr = 140,000, 145,000, and 150,000 were isolated from a partially-purified preparation of 10S DNA polymerase alpha. On the other hand, the polypeptides with Mr = 150,000, 180,000, and 240,000 were obtained from a crude extract of calf thymus. Tryptic peptide maps showed that the large polypeptides with Mr = 150,000, and 180,000 were very similar in primary structure and that the structures of Mr = 180,000 and 240,000 polypeptides contained partially common sequences. Among these polypeptides, the Mr = 150,000 polypeptide was shown to correlate with the enzyme activity. These results suggest that the large polypeptide of 10S DNA polymerase alpha is initially synthesized as Mr = 180,000 or larger polypeptide, then converted to the form with Mr = 150,000. The Mr = 140,000 and 145,000 polypeptides in the purified preparation may be artificial products formed during purification.

Purification and immunological characterization of DNA polymerase-alpha from human acute lymphoblastic leukemia cells

DNA polymerase-alpha was purified from the cytosol of blast cells of a patient with acute lymphoblastic leukemia by ammonium sulfate fractionation and successive column chromatographies. The purified enzyme had a specific activity of 2943 units/mg protein with activated calf thymus DNA as a template. The enzyme sediments under high-salt conditions as a homogeneous band at 7.2 S and free from other DNA polymerases (beta, gamma) and terminal deoxynucleotidyl transferase activity. The native molecular weight of the enzyme from gel filtration and glycerol gradient centrifugation was found to be 175 000. The values of Stokes radius (53 A), diffusion coefficient (4.05 x 10(-7) cm2/s) and frictional ratio (1.42) determined by gel filtration suggest that the native enzyme is compact and globular. Antibodies to DNA polymerase-alpha were raised in rabbits. These antibodies, partially purified by 50% ammonium sulfate saturation and Sephadex G-200 chromatography, gave one precipitin band on immunodiffusion and inactivate DNA polymerase-alpha-. This antibody preparation also inhibited, in vitro, the activity of DNA polymerase-alpha from calf thymus, phytohemagglutinin-stimulated normal human lymphocytes, as well as that from other leukemic cells. Thus, DNA polymerase-alpha from calf thymus and human leukemic cells resemble each other in antibody specificity.

Differential inhibition of multiple forms of DNA polymerase alpha from IMR-32 human neuroblastoma cells

Three forms of DNA polymerase (pol) alpha from human neuroblastoma IMR-32 were separated by DEAE column chromatography. All sedimented at approximately 7 S in 5-20% continuous sucrose density gradients. All were heat labile, with pol alpha 2 the most (90% inactivated) and pol alpha 3 the least (50% inactivated) sensitive to heating for 5 min at 50 degrees C. pol alpha 1 and alpha 2 efficiently utilized activated calf thymus DNA as template. The most active form, pol alpha 2, used both poly(dA).(dT)12-18 and poly(dT).(dA)12-18 as template at equal rates. Differential inhibition of DNA polymerase alpha activities was examined in the presence of ricin, hemin, and a nonhistone chromatin protein. All three polymerases were inhibited by both ricin (nonreduced) and hemin, with pol alpha 2 the most (80-90%) and pol alpha 3 the least (60%) sensitive in each case. In contrast, only pol alpha 2 and alpha 3 activities were inhibited (80-85%) by rat liver nonhistone chromatin protein.

Unique requirements for template primers of DNA polymerase beta from rat ascites hepatoma AH130 cells

The optimal condition for the rat DNA polymerase beta activity with (rA)n . (dT)12-18 as a template-primer was determined. The activity was remarkably affected by the concentration of the primer, (dT)12-18' and the mixing ratio of (dT)12-18 to (rA)n. DNA polymerase beta requires higher primer concentration (Km = 11.1 microM with respect to 3'-OH of the primer) than DNA polymerase gamma (Km = 0.04 microM) or oncornaviral DNA polymerase (Km = 0.08 microM) and the enzyme represented the maximum activity in the base ratio of 2:1 with (dT)12-18 and (rA)n suggesting the difference in reaction mechanisms of these enzymes. Under the optimized conditions, the specific activity of the near homogeneous preparation of DNA polymerase beta was 1,000,000 units per mg protein.