An Arabidopsis thaliana protein homologous to cyanobacterial high-light-inducible proteins

An Arabidopsis thaliana cDNA clone encoding a novel 110 amino acid thylakoi d protein has been sequenced. The in vitro synthesized protein is taken up by intact chloroplasts, inserted into the thylakoid membrane and the transi t peptide is cleaved off during this process. The mature protein is predict ed to contain 69 amino acids, to form one membrane-spanning alpha-helix and to have its N-terminus at the stromal side of the thylakoid membrane. The protein showed similarity to the LHC, ELIP and PsbS proteins of higher plan ts, but more pronounced to the high-light-inducible proteins (HLIPs) of cya nobacteria and red algae, to which no homologue previously has been detecte d in higher plants. As for HLIP and ELIP, high light increases the mRNA lev els of the corresponding gene. Sequence comparisons indicate that the prote in may bind chlorophyll and form dimers in the thylakoid membrane. The leve l of expression of the protein seems to be far lower than that of normal PS I and PSII subunits.