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

摘要

Expression of the crhR gene for an RNA helicase, CrhR, is strongly induced when the cyanobacterium Synechocystis sp. PCC 6803 is exposed to a downward shift in ambient temperature. CrhR might be involved in the acclimation of cyanobacterial cells to low-temperature environments but its putative role during such acclimatization is unknown. In the present study, we replaced the crhR gene with a spectinomycin-resistance gene cassette. The resultant {triangleup}crhR cells grew more slowly than wild-type cells at low temperatures. DNA microarray analysis of the genome-wide expression of genes and Northern and Western blotting analyses indicated that such mutation of the crhR gene repressed the low-temperature-inducible expression of the chaperone-encoding heat-shock genes groEL1 and groEL2 at both the transcriptional and the translational level. The kinetics of changes in levels of the groESL transcript and the groEL2 transcript after addition of rifampicin suggested that CrhR might stabilize these transcripts during the early phase, namely, from 5 to 60 min after the start of acclimatization to low temperature, and enhanced the transcription of these genes two to four hours later, namely, at 3-5 h. Our results indicate that CrhR regulates the low-temperature-induced expression of these molecular chaperones, which, in turn, might be essential for acclimatization of Synechocystis cells to low temperatures.