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Enzyme induction in a temperature-sensitive cell cycle mutant of chinese hamster fibroblasts

✍ Scribed by Fyllis Landy-Otsuka; Immo E. Scheffler

Publisher
John Wiley and Sons
Year
1980
Tongue
English
Weight
901 KB
Volume
105
Category
Article
ISSN
0021-9541

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✦ Synopsis

Abstract

A temperature‐sensitive (ts) cell cycle mutant of Chinese hamster fibroblasts with a block in G~1~ was investigated. Attention was on the expression of the activity of three enzymes: ornithine decarboxylase (ODC), S‐adenosylmethionine decarboxylase (SAMDC), and thymidine kinase (TK). ODC and SAMDC activities are normally induced in the middle of, or late in, the G~1~ phase, while TK activity starts to appear at the G~1~/S boundary. In the ts mutant released from serum starvation at the nonpermissive temperature (40.8°C), we find no effect on the expression of SAMDC activity, a significantly reduced level of ODC activity compared to the control at the permissive temperature (34°C), and no induction of TK activity. Results presented here and in a previous publication (Landy‐Otsuka and Scheffler, '78) suggest that the decrease in ODC activity is due to an effect of the nonpermissive temperature on a post‐transcriptional step, possibly a very rapid inactivation of the enzyme. The absence of TK activity, on the other hand, appears to be due to a block in transcription at the nonpermissive temperature.

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