Expression of two alternative sigma factors of Synechococcus sp. strain PCC 7002 is modulated by carbon and nitrogen stress

Abstract

The sigB and sigC genes, encoding two alternative sigma factors of the unicellular marine cyanobacterium Synechococcus sp. PCC 7002, were cloned and characterized. Strains in which the sigB and sigC genes were insertionally inactivated were viable under standard laboratory conditions, indicating that SigB and SigC are group 2 sigma factors. Starvation for either nitrogen or carbon caused an increase in sigB mRNA levels. Transcripts for the sigC gene initially increased but then decreased during nitrogen and carbon starvation. The SigC protein could not be identified in cyanobacterial extracts using antisera to Synechococcus sp. PCC 7002 SigA or RpoD from Bacillus subtilis. The ratio of the principaf vegetative sigma factor, SigA, to SigB decreased during either nitrogen starvation or carbon starvation, and the levels of SigB also increased in the sigC mutant strain. These results imply that SigB and SigC play roles in modifying transcription in response to changes in carbon and nitrogen availability in this cyanobacterium.

SigC, the Group 2 Sigma Factor of RNA Polymerase, Contributes to the Late-stage Gene Expression and Nitrogen Promoter Recognition in the CyanobacteriumSynechocystissp. Strain PCC 6803

“…[12][13][14][15][16][17][18][19][20] However, the functional assignments and roles of relevant sigma factors are still not clear in y To whom correspondence should be addressed. Tel/Fax: +81-29-888-8651; E-mail: asam@mx.ibaraki.ac.jp cyanobacteria.…”

Characterization of Single and Double Inactivation Strains Reveals New Physiological Roles for Group 2 σ Factors in the Cyanobacterium Synechocystis sp. PCC 6803

“…PCC 7120 (Khudyakov and Golden, 2001), Synechococcus sp. PCC 7002 (Caslake et al, 1997), and Synechococcus sp. PCC 7942 (Goto- Seki et al, 1999) as well as double inactivation strains in Synechocystis (Fig.…”

Group 3 sigma factors in the marine cyanobacterium Synechococcus sp. strain PCC 7002 are required for growth at low temperature

“…It is well known that multiple group 2 sigma factors are present in cyanobacteria (Brahamsha and Haselkorn, 1992;Campbell et al, 1998;Caslake et al, 1997;Gruber and Bryant, 1998;Tanaka et al, 1992). These non-essential sigma factors are thought to modulate the transcription genes, including the sigma factor genes themselves, whose expression levels change upon changing nutrient conditions for nitrogen, carbon or sulfur (Asayama et al 2004;Brahamsha and Haselkorn, 1992;Caslake et al, 1997;Gruber and Bryant, 1998;Imamura et al, 2006;Khudyakov and Golden, 2001;Muro-Pastor et al, 2001;Osanai et al, 2005).…”

“…These non-essential sigma factors are thought to modulate the transcription genes, including the sigma factor genes themselves, whose expression levels change upon changing nutrient conditions for nitrogen, carbon or sulfur (Asayama et al 2004;Brahamsha and Haselkorn, 1992;Caslake et al, 1997;Gruber and Bryant, 1998;Imamura et al, 2006;Khudyakov and Golden, 2001;Muro-Pastor et al, 2001;Osanai et al, 2005). In other cases, these sigma factors are required for circadian expression of genes including psbA1 (Tsinoremas et al, 1996).…”

“…strain PCC 7002 and five genes encoding group 1 and 2 sigma factors, designated sigA, sigB, sigC, sigD and sigE have been isolated and characterized in this marine cyanobacterium. Two group 2 sigma factors, SigB and SigC, have roles in modifying transcription in response to changes in carbon and nitrogen availability (Caslake et al, 1997), while SigE is involved in the transcription of post-exponential-phase-specific gene expression in Synechococcus sp. strain PCC 7002 (Gruber and Bryant, 1998).…”