DnaK3, one of the three DnaK proteins of cyanobacterium Synechococcus sp. PCC7942, is quantitatively detected in the thylakoid membrane.

Subcellular localization of three DnaK proteins of cyanobacterium Synechococcus sp. PCC7942 was determined. DnaK1 and DnaK2 proteins were detected mainly in the cytosolic fraction. On the other hand, the DnaK3 protein occurred in large amounts in the thylakoid membrane fraction. Furthermore, DnaK3 was found to be located on the surface of the thylakoid membrane on the cytosol side. Subcellular localization of chimeric and truncated DnaK3 proteins was also determined, and it was suggested that the region a.a. 381 to a.a. 597 of DnaK3 protein, which is considered to correspond to the peptide-binding domain, was required for the association with the thylakoid membrane.