Correlation of some published amino acid sequences for photosystem I polypeptides to a 17 kDa LHCI pigment-protein and to subunits III and IV of the core complex

Abstract

Photosystem I (PSI) in barley consists of at least 11 polypeptides of which three have apparent sizes of 15-19 kDa. Two of these polypeptides (subunits III and IV) are constituents of the core complex (CCI), the third is a component of the light-harvesting complex (LHCI). After fractionation of PSI into its CCI and LHCI components, each of the polypeptides has been isolated and its N-terminal region sequenced. We conclude that the gene sequence published for subunit IV of spinach [(1988) FEBS Lett. 237, 108-112] is not that of subunit IV but rather that of the 17 kDA LHCIc pigment protein. We confirm that the published sequence for subunit III [(1988) Curr. Genet. 14, 511-518] is indeed that of subunit III; seemingly conflicting identifications, based on apparent sizes on SDS-PAGE, of which polypeptides are subunits III and IV are probably explained by subunit III's electrophoretic migration rate being dependent on the solvent.