Sequence and analysis of a dnaJ homologue gene in cyanobacterium Synechococcus sp. PCC7942

The chromosomal region containing a dnaJ gene homologue (dnaJ7942) was sequenced from unicellular cyanobacterium Synechococcus sp. PCC7942. The dnaJ7942 gene as well as following two orfs are located in the region immediately downstream of dnaK3, and they seem to be cotranscribed. The dnaJ7942 gene product shares, like all J homologues, homology for the highly conserved "J-domain" of DnaJ. It does not have, however, a glycine and phenylalanine (G/F)-rich region nor cysteine (Cys)-rich region unlike the Escherichia coli DnaJ protein. When this gene was expressed in E. coli, cells became filamentous in contrast to those expressing the E. coli dnaJ gene. Gene disruption experiments indicated that the dnaJ7942 gene was essential for growth. Analysis of subcellular localization revealed that the DnaJ protein is mainly located on the thylakoid membrane in the cyanobacterium.