AsnC, a multifunctional regulator of genes located around the replication origin of Escherichia coli, oriC.

The expression of the gidA gene which is located immediately counterclockwise of the replication origin of Escherichia coli, oriC, was found to be negatively regulated by the AsnC protein in an in vitro transcription-translation system. This effect is not due to simple repression of transcription originating at the gidA promoter, because the AsnC protein did not change the level of gidA promoter dependent transcription as analysed by promoter-galK fusions and by S1 mapping. From these data we conclude that the AsnC protein controls gidA gene expression at a post-transcriptional level. gidA is the third gene in the oriC region, besides asnA and asnC, whose expression is under AsnC control. However, the mechanisms involved are different: regulation of transcription in the case of asnA and asnC and post-transcriptional control of gidA. The gidA promoter was mapped by deletion analysis and by S1 mapping. We defined two regions that affect promoter activity negatively. Additional transcripts, regulated by AsnC, started more than 300 bp upstream of the gidA promoter and were found to enter the gidA region. These transcripts, originating either at the mioC and/or the ansC promoter traverse the replication origin.