Novobiocin sensitivity and chromatin conformation in wild-type and temperature-sensitive mouse L cells

Abstract

The ts A1S9 cell is a dnats mutant of mouse L cells which exhibits enhanced sensitivity to killing by the antibiotic novobiocin, as compared with the parental wild-type (WT-4) cell, another dnats mouse L cell (ts C1), and other mammalian cells. Such a response was not detected with other cytotoxic agents tested. Novobiocin inhibits DNA synthesis in ts A1S9 cells, at concentrations which have little or no effect on RNA or protein synthesis. Enhanced novobiocin sensitivity is not due to altered cellular permeability to the drug, since ts A1S9 cells do not take up more antibiotic than do WT-4 or ts+ AR mouse L cells. A ts+ revertant of ts A1S9 cells exhibits a wild-type pattern of novobiocin sensitivity, suggesting that novobiocin resistance may be encoded in the ts A1S9 locus. These findings led to a study of DNA conformation which revealed that the nuclear, chromatin-bound DNA of temperature-inactivated ts A1S9 cells sediments differently in ethidium bromide sucrose density gradients than does that of WT-4 cells grown at 38.5 °C. These observations suggest that expression of the ts A1S9 defect results in a more highly constrained conformation of the DNA, relative to that in control cells, and that in this configuration the DNA may be unable to act as template for replication.