The activities of DNA polymerases alpha, beta and gamma were determined in mouse liver as a function of age by a combination of glycerol density gradient centrifugation with polymerase specific assays. Although alpha polymerase was preserved throughout the life span, the activity dropped sharply from a high level at the fetal and neonatal stages to a level one order lower after maturation through adjustment of the amount of protein administered. beta polymerase showed similar but less drastic changes than alpha. DNA polymerase gamma activity increased about two-fold in going from newborn to adult stages and remained constant after maturation. According to the amount of DNA, DNA polymerase alpha decreased after birth, but the change was less drastic compared to that through adjustment of the amount of protein. DNA polymerase beta increased the activity 2-3-fold within a period of 3 months following birth. gamma polymerase underwent more than a 10-fold increase in activity through adjustment of the amount of DNA within the same period.

Aging↗

PubMedDate not supplied

Effects of diesel exhaust particles on chromosome aberration, sister chromatid exchange and morphological transformation in cultured mammalian cells.

The ability of diesel exhaust particles (diesel tar) from light-duty (LD) and heavy-duty (HD) engines to induce chromosome aberrations, sister chromatid exchanges (SCEs) and morphological transformations is examined. Chinese hamster V79 cells were treated with LD and HD diesel tar for 3 h in order to analyze chromosome aberrations and SCEs. BALB/c 3T3 cells were used for the morphological transformation test. LD tar induced significant numbers of chromosome aberrations, whereas HD did not. Both LD and HD samples increased the number of SCEs in a dose-dependent fashion, with LD being more potent. In the transformation test, LD tar also induced a significant number of Type III foci, while HD was only weakly active. The transformed cells isolated from these Type III foci produced tumors when injected into nude mice. These results show that LD possesses clear clastogenic and transforming capabilities but that HD is weaker in this regard.

Animals↗