Abstract
Cyanobacteria constitute a remarkable group of prokaryotes, not only having an oxygen-producing photosynthetic system but also showing unique conservation of molecular chaperone gene structures. To reveal the features of cyanobacterial stress proteins, we have studied major molecular chaperone family, Hsp70/DnaK, Hsp40/DnaJ and Hsp90/HtpG.
In the cyanobacterium Synechococcus elongatus PCC 7942 genome, three dnaK and four dnaJ homologs were identified. We analyzed their expression profile upon various stresses. Then we found that a conserved sequence, located in the upstream of several hsp genes exclusively in cyanobacteria, was indispensable for the expression of stress responding dnaK gene.
Moreover, we carried out yeast two-hybrid screening to explore the function of Hsps and found out several specific interactions. Those were between DnaJ and RNase E, which is an essential endoribonuclease, and HtpG and HemE, which is a metabolic enzyme of tetrapyrrole biosynthetic pathway. These findings suggest novel functions of Hsps in cyanobacteria.
