LOCALIZATION AND CHARACTERIZATION OF A NOVEL 20 KDA POLYPEPTIDE IN THE CHLOROPLAST OF THE GREEN-ALGA DUNALIELLA-SALINA

Recent work with the green alga Dunaliella salina showed the presence of a similar to 20 kDa chloroplast protein that was recognized by poly clonal antibodies raised against the isolated LHC-II [Webb M.R. and Me lis A. (1995) Plant Physiol. 107:885]. In this report, a characterizat ion of the similar to 20 kDa polypeptide is presented. It is shown tha t it is localized in the chloroplast envelope membrane of D. salina. T he abundance of this protein is constant on a per cell basis and indep endent of the light regime during cell growth. The similar to 20 kDa p olypeptide is easily degraded to a similar to 19 kDa product during sa mple preparation. A limited amino acid sequence of 21 residues from th e free N-terminus of the similar to 19 kDa product was obtained. On th e basis of this partial sequence, it was concluded that the similar to 20 kDa polypeptide is not a degradation product of a known LHC-II but rather a novel protein. The similar to 20 kDa polypeptide did not cro ss-react with antibodies raised against the Cbr (carotene biosynthesis -related) gene product and showed a different electrophoretic mobility from the latter. Light-shift experiments suggest that the similar to 20 kDa polypeptide is not an ELIP (early light-inducible protein). Pos sible functions of the similar to 20 kDa protein are discussed.