INDUCTION AND REPAIR OF CYCLOBUTANE PYRIMIDINE DIMERS IN THE ESCHERICHIA-COLI TRANSFER-RNA GENE TYRT - FIS PROTEIN AFFECTS DIMER INDUCTION IN THE CONTROL REGION AND SUPPRESSES PREFERENTIAL REPAIR IN THE CODINGREGION OF THE TRANSCRIBED STRAND, EXCEPT IN A SHORT REGION NEAR THE TRANSCRIPTION START SITE

We analysed induction and repair of UV induced pyrimidine dimers in th e Escherichia coil tRNA gene tyrT. In wild-type (WT) log or stationary phase different patterns of induction occurred in the three Fis bindi ng sites and the core promoter -35 sequence of the control region: thi s was absent in fis(-) cells. In stationary WT cells, slow, similar ra tes of repair occurred throughout the non-transcribed strand (NTS). Fa ster repair occurred in the NTS control region in WT log phase. NTS re pair in fis(-) cells was similar, except the control region differed l ess between phases. Heterogeneous repair occurred along the transcribe d strand (TS). Ln the control region repair was faster than in the NTS . Repair in the TS coding region changed between growth phases or if r epair took place in different media. When irradiated log phase WT cell s were in rich medium, two TS domains were evident: a fast-repaired do main within 31 nucleotides from the transcription start site; and a mo re slowly repaired domain composed of the rest of the TS. A sharp grad ient existed in the small domain with very fast repair at the beginnin g and diminished repair towards the end. Fast transcription coupled re pair (TCR) in the small domain was absent in the TS large domain, wher e repair was similar to the NTS and to the entire TS in mfd(-) cells. Ln similarly treat-ed stationary phase WT cells, TCR occurred in the l arge domain. Depletion of Fis reinstates TCR to a lesser extent, whils t a substitution of five nucleotides at the Fis binding sites in the u pstream activating sequence reinstates TCR. Reinstatement of TCR was a lso achieved by incubating irradiated WT cells in minimal salt medium without the required amino acid. Our results suggest that Fis indirect ly suppresses preferential repair in the TS large domain by stimulatin g transcription. (C) 1997 Academic Press Limited.