Purified lexA protein is a repressor of the recA and lexA genes.
Open Access
- 1 July 1981
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 78 (7), 4199-4203
- https://doi.org/10.1073/pnas.78.7.4199
Abstract
Escherichia coli shows a pleiotropic response (the SOS response) to treatments that damage DNA or inhibit DNA replication. Previous evidence has suggested that the product of the lexA gene is involved in regulating the SOS response, perhaps as a repressor, and that it is sensitive to the recA protease. We show here that lexA protein is a repressor of at least two genes, recA and lexA. Purified protein bound specifically to the regulatory regions of the two genes, as judged by DNase I protection experiments, and it specifically inhibited in vitro transcription of both genes. The binding sites in recA and lexA were found to be about 20 base pairs (bp) and 40 bp long, respectively. The 40-bp sequence in lexA was composed of two adjacent 20-bp sequences, which had considerable homology to one another and to the corresponding recA sequence. These 20-bp sequences, which we term "SOS boxes," show considerable inverted repeat structure as well. These features suggest that each box represents a single repressor binding site. Finally, we found that purified lexA protein was a substrate for the recA protease in a reaction requiring ATP or an analogue, adenosine 59-[gamma-thio]triphosphate, and denatured DNA.This publication has 38 references indexed in Scilit:
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