| Popis: |
The effect of prolonged treatment of CHO Chinese hamster or Microtus agrestis cells with amethopterin or 5-fluorodeoxyuridine on the DNA replicator site distribution and on cell survival has been investigated with EM autoradiography of nuclear sections and cell cycle studies. A pool of DNA precursors in the CHO cells allows slow progression of G1 cells through the first S period with a normal homogeneous replicator site distribution in early-S, cell survival is normal. After mitosis cells are blocked at the beginning of the second S period with replicator sites now distributed on the nuclear membrane and nucleolar periphery. Degenerative changes rapidly occur, cell recovery is delayed and survival is reduced on release from the inhibition. Microtus cells with no pool of precursors show normal replicator site distribution when labelled in exponential growth. After inhibition however, cells do not progress through the S period and show early peripheral distribution of replicator sites and early degenerative changes. This peripheral distribution probably represents DNA breakdown. It is proposed that small replicating fragments are produced, and accumulate on the nuclear membrane and around the nucleolus during the process of thymineless death. |
