Abstract
In cyanobacteria, a disruptant of hspA encoding a small heat shock protein homologue, shows decreased cell growth rates at moderately high temperatures, and loss of both basal and acquired thermo-tolerances, which resemble the phenotype of a disruptant of htpG (encoding an Hsp90 homologue). In vitro studies have shown that one of the major functions of small heat shock proteins and Hsp90 is to bind and keep non-native proteins in a refolding-competent state, under denaturing conditions. The aim of the present study is to elucidate whether constitutive expression of HspA can functionally replace HtpG in the cyanobacterium Synechococcus sp. PCC 7942. HspA neither improved the growth of the htpG disruptant at 45oC nor conferred thermo-tolerance to the mutant. These results suggest that cellular function of HtpG may differ significantly from that of HspA. Experiments are in progress to identify targets of HtpG.
