sp. Strain PCC 6803 Involved in Survival under Nitrogen Stress

The expression of sll1689, an open reading frame from the cyanobacterium Synechocystis sp. strain PCC 6803 putatively encoding a member of the s70 family of sigma factors, appears to be regulated by the nitrogen control transcription factor NtcA. Disruption of sll1689 had no noticeable effect on exponential growth, identifying its product as a member of the group 2, nonessential class of s70-like sigma factors; however, this disruption decreased the viability of the cells after long periods of nitrogen starvation. We have named this gene rpoD2-V. The expression of glnN, encoding a type III glutamine synthetase, was impaired in strains bearing an inactivated copy of the rpoD2-V gene. Eubacterial RNA polymerase consists of a core enzyme and a sigma factor that directs the complex to a specific class of promoter sequences. Most eubacterial genomes encode a number of different sigma factors that recognize different sub-sets or groups of promoters. This variety of sigma factors allows basal expression of certain genes as well as regulated expression of other genes in response to environmental or developmental signals (44). Two families of sigma factors hav