Physiology of the SOS response: Kinetics of lexA and recA transcriptional activity following induction
✍ Scribed by Markham, Bruce E. ;Harper, Joan E. ;Mount, David W.
- Publisher
- Springer
- Year
- 1985
- Tongue
- English
- Weight
- 669 KB
- Volume
- 198
- Category
- Article
- ISSN
- 0026-8925
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✦ Synopsis
The products of the lexA and recA genes play central roles in the regulation of the Escherichia coli SOS response. We have measured the rate of mRNA synthesis from each gene at intervals following various inducing treatments in order to obtain a more precise timing of the induction process. Further, we provide quantitative evidence for kinetics of decay from fully induced levels of mRNA synthesis to basal levels as the cells shut down the SOS response which are in agreement with previously published data on the expression of specific SOS functions. The induction kinetics of lexA and recA gene expression are parallel except for nalidixic acid (NAL) treatment, with the actual levels of lexA mRNA synthesis being about 10-fold lower than that of recA. Reestablishment of repression from RecA commenced over 30 min earlier than from lexA. These results are fully consistent with the model that the functions result from the increased gene expression.
promoted cleavage (Little 1984). One or more signal molecules are required to stimulate protease activity in vivo which may include nucleotides, oligonucleotides, damaged single or double stranded DNA (Oishi and Smith 1978;Smith and Oishi 1978; Irbe and Oishi ]980; Craig and Roberts 1980, 1981;Phizicky and Roberts 1981). The signal disappears at a time after inducing treatment which appears to correspond with the completion of DNA repair (Gudas and Mount 1977;Markham and Brubaker 1980). This disappearance results in the decline of protease activity, the reappearance of functional lexA repressor and the re-establishment of repression of SOS genes.
According to the SOS regulatory system, the rate of SOS gene transcription increases after repressor cleavage begins, remains high as long as cleavage occurs, and then decreases to a normal level as cleavage subsides and repressor accumulates. The rate of recA mRNA synthesis has been shown to increase after u.v. induction but a subsequent