An RNA helicase, CrhR, regulates the low-temperature-inducible expression of heat-shock genes groES, groEL1 and groEL2 in Synechocystis sp. PCC 6803

1 Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500 046, India 2 National Institute for Basic Biology (NIBB), Okazaki 444-8585, Japan 3 Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan 4 Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India The crhR gene for RNA helicase, CrhR, was one of the most highly induced genes when the cyanobacterium Synechocystis sp. PCC 6803 was exposed to a downward shift in ambient temperature. Although CrhR may be involved in the acclimatization of cyanobacterial cells to low-temperature environments, its functional role during the acclimatization is not known. In the present study, we mutated the crhR gene by replacement with a spectinomycin-resistance gene cassette. The resultant crhR mutant exhibited a phenotype of slow growth at low temperatures. DNA microarray analysis of the genome-wide expression of genes, and Northern and Western blotting analyses indicated that mutation of the crhR gene repressed the low-temperature-inducible expression of heat-shock genes groEL1 and groEL2 , at the transcript and protein levels. The kinetics of the groESL co-transcript and the groEL2 transcript after addition of rifampicin suggested that CrhR stabilized these transcripts at an early phase, namely 5–60 min, during acclimatization to low temperatures, and enhanced the transcription of these genes at a later time, namely 3–5 h. Our results suggest that CrhR regulates the low-temperature-inducible expression of these heat-shock proteins, which, in turn, may be essential for acclimatization of Synechocystis cells to low temperatures. Correspondence Norio Murata murata{at}nibb.ac.jp Five supplementary figures are available with the online version of this paper.