Proteomic Characterization of the Chlamydomonas reinhardtii Chloroplast Ribosome

Abstract

We have conducted a proteomic analysis of the 70 S ribosome from the chloroplast. Twenty-seven orthologs of large subunit proteins were identified in the 50 S subunit, as well as an ortholog of the spinach plastid-specific ribosomal protein-6. Several of the large subunit proteins of have short extension or insertion sequences, but overall the large subunit proteins are very similar to those of spinach chloroplast and . Two proteins of 38 and 41 kDa, designated RAP38 and RAP41, were identified from the 70 S ribosome that were not found in either of the ribosomal subunits. Phylogenetic analysis identified RAP38 and RAP41 as paralogs of spinach CSP41, a chloroplast RNA-binding protein with endoribonuclease activity. Overall, the chloroplast ribosome of is similar to those of spinach chloroplast and , but the ribosome has proteins associated with the 70 S complex that are related to non-ribosomal proteins in other species. In addition, the 30 S subunit contains unusually large orthologs of S2, S3, and S5 and a novel S1-type protein (Yamaguchi, K. , (2002) Plant Cell 14, 2957–2974). These additional proteins and domains likely confer functions used to regulate chloroplast translation in .