Roles of molecular chaperones for regulation of genes and assembly of photosynthetic apparatus

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1.A positive control of the cyanobacterial groESL1 transcription by a novel molecular chaperone, Orf7.5Orf7.5 was a positive transcription factor which increases the activity of the groESL1 promoter of Synechococcus sp. PCC 7942 especially under heat shock conditions by interacting with the major sigma factor.2.Post-transcriptional regulation of the cyanobacterial hspA heat-shock inductionThe hspA gene from Synechococcus vulcanus encodes a small heat-shock protein. We showed that the hspA heat-shock induction is self-controlled post-transcriptionally.3.Cellular functions of HspAComparative analyses of the wild-type Synechocystis sp. PCC 6803 and its hspA null mutant strain showed that hspA is involved in salt-stress management. The role of HspA under stress conditions was investigated comparing Synechococcus strain ECT16-1, which constitutively expresses HspA, with the reference strain ECT. HspA conferred the cyanobacterium ultrastructural stability under high temperature or intensive … More light stress.4.Cellular functions of HtpGWe elucidated whether constitutive expression of HspA can functionally replace HtpG in Synechococcus sp. PCC 7942. It did not improve defects of an htpG mutant under stress conditions, indicating that cellular function of HtpG may differ from that of HspA.5.Roles of molecular chaperone for the phycobilisome assemblyWe showed that HspA interacts directly with phycocyanins from Synechococcus sp. PCC 7942 in vitro. We also showed a specific interaction between a linker polypeptide of phycobilisome and HtpG These results indicate that the molecular chaperones play important roles in the phycobilisome assembly by stabilizing phycocyanins and the linker polypeptide.6.Roles of the cyanobacterial isiABC operon in protection from oxidative and heat stressesThe isiAB operon encodes CP43' and flavodoxin which form the photosynthetic apparatus. We showed that the isiABC operon plays essential roles not only under iron stress, but also under multiple stresses such as oxidative and heat stresses. Less