A cyanobacterial gene encoding an ortholog of Pirin is induced under stress conditions.

Pirin is a recently identified protein in eukaryotes as a transcription cofactor or as an apoptosis-related protein. Although Pirin is highly conserved from bacteria to human, there have been no reports on prokaryotic Pirin orthologs. We show here that pirA (sll1773) encoding an ortholog of Pirin together with an adjacent gene, pirB (ssl3389), was upregulated under high salinity and some other stress conditions in a cyanobacterium Synechocystis sp. PCC 6803. Induction of the pirAB genes was not related to cell death and disruption of pirA did not affect the gene expression profile. Expression of the pirAB genes was negatively regulated by a LysR family transcriptional regulator encoded by pirR (slr1871) located immediately upstream of pirAB in the divergent direction. DNA microarray analysis indicated that PirR repressed expression of closely located ORFs, slr1870 and mutS (sll1772), in addition to pirAB and pirR itself.