title: In vitro synthesis and processing of a putative precursor for the small subunit of ribulose-1,5-bisphosphate carboxylase of Chlamydomonas reinhardtii.
abstract: Translation of polyadenylated mRNA of Chlamydomonas reinhardtii in a cell-free wheat germ system resulted in the synthesis of numerous discrete polypeptides. Among them was a species with molecular weight 20,000 that was immunoprecipitated specifically by antibodies raised against the authentic small subunit (16,500 daltons) of ribulose-1,5-bisphosphate carboxylase [3-phospho-D-glycerate carboxy-lyase(dimerizing), EC 4.1.1.39]. Since the immunoprecipitated polypeptide has a larger molecular weight by approximately 3500 than the small subunit (S) it was identified as a putative biosynthetic precursor (pS). Post-translational conversion of pS by a specific endoprotease yielded two detectable products: one apparently identical in size to S and the other, a small peptide, presumably representing the remainder of pS. The endoprotease requires sulfhydryl groups for its activity and is present in a C. reinhardtii postribosomal supernatant as well as in a free polysome fraction. The latter could account for the observation that completion of nascent chains in free polysomes yielded S but not pS. We propose that pS is an extrachloroplastic form of S and that the small peptide portion plays a role in the transfer of S into the chloroplast.
mesh_terms: D002262:Carboxy-Lyases / Q000096:biosynthesis*; D002474:Cell-Free System; D002696:Chlamydomonas / Q000201:enzymology; D002736:Chloroplasts / Q000201:enzymology; D010450:Endopeptidases / Q000378:metabolism; D004792:Enzyme Precursors / Q000378:metabolism*; D008970:Molecular Weight; D012333:RNA, Messenger / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000096:biosynthesis*
chemical_list: D004792:Enzyme Precursors; D012333:RNA, Messenger; D010450:Endopeptidases; D002262:Carboxy-Lyases; D012273:Ribulose-Bisphosphate Carboxylase
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