Low‐molecular‐mass proteins in cyanobacterial photosystem II: Identification ofpsbH andpsbK gene products by N‐terminal sequencing

Abstract
The O2‐evolving photosystem II core complex was isolated from a thermophilic cyanobacterium,Synechococcus vulcanusCopeland. Analysis by SDS‐polyacrylamide gel electrophoresis revealed that the complex contained at least seven low‐molecular‐mass proteins in addition to the well characterized CP47 apoprotein, CP43 apoprotein, 33 kDa extrinsic protein, D1 protein, D2 protein and large subunit of cytochromeb‐559. The separation profiles of these low‐molecular‐mass proteins were very similar between cyanobacterial and higher plant PS II. N‐terminal sequences of the 6.5 kDa and 3.9 kDa proteins of cyanobacterial core complex were determined after blotting to a polyvinylidene difluoride membrane. The sequence of the 6.5 kDa protein showed high homology with an internal sequence of plantpsbH gene product, so‐called 10 kDa phosphoprotein, but did not conserve the Thr residue which is specifically phosphorylated in plants. The sequence of the 3.9 kDa protein corresponded to the K protein of higher plants (mature form ofpsbK gene product). These results indicate that the products of bothpsbH andpsbK genes are present in cyanobacterial PS II as well as being associated with the O2‐evolving core complex.