Possible transcriptional control of three polypeptides which accumulate in a temperature-sensitive mammalian cell line

Abstract

THE availability of well characterised conditional lethal mutants will widen our knowledge of the genetics and physiology of mammalian cells. Temperature-sensitive mutants (ts mutants) have been very useful in studies carried out in a great variety of systems from microorganisms to Drosophila. We have undertaken the characterisation of a ts mutant (K12) isolated by Roscoe et al.¹ from the established line of Chinese hamster fibroblasts WglA. The K12 mutant has two interesting properties: it is a cell-cycle mutant^2,3, having its execution step (the time during which the mutated function is required by the cells in order to progress through the cell cycle) during the 4 h preceding the initiation of the S phase; and the synthesis of three specific cellular polypeptides is enhanced when the cells are incubated at the non-permissive temperature (40.5 °C) (J.A.M. and V. Fincham, unpublished). These polypeptides, called A, B and C, are not affected in other ts mutants defective for the initiation of the S phase and in hybrids in which the K12 mutation is complemented. These data suggest that the K12 mutant is affected in some function necessary both for the commitment of the cells to new rounds of DNA replication and for the regulation of A, B and C polypeptide synthesis. We now present evidence, obtained by investigating the effect of actinomycin D on the proteins synthesised by K12 cells, incubated at the non-permissive temperature and by synthesising the proteins in vitro, that the synthesis of these proteins is regulated at the transcriptional level.