N‐terminal sequence analysis of the 8 kDa protein in<i>Chlamydomonas reinhardii</i>Localization of the phosphothreonine

Abstract

A phosphorylated 8 kDa protein of Chlamydomonas reinhardii thylakoids has been isolated and its N‐terminal amino acid sequence determined by gas‐phase sequencing. The sequence analysis of the 48 amino acid residues revealed that this protein is about 50% homologous to the psb H gene products of higher plants. In contrast to them, it contains an insert of seven amino acid residues (Ser‐5 to Lys‐11). The first threonine residue was phosphorylated as determined by 32 P detection during sequencing and also by analysis of the modified degradation products in the chemical reaction of the Edman degradation process. This latter method allows the identification of phosphorylated threonine residues without radiolabelling the protein.