title: Light-regulated translation of chloroplast proteins. I. Transcripts of psaA-psaB, psbA, and rbcL are associated with polysomes in dark-grown and illuminated barley seedlings.
abstract: We have previously observed (Klein, R. R., and J. E. Mullet, 1986, J. Biol. Chem. 261:11138-11145) that translation of two 65-70-kD chlorophyll a-apoproteins of Photosystem I (gene products of psaA and psaB) and a 32-kD quinone-binding protein of Photosystem II (gene product of psbA) was not detected in plastids of dark-grown barley seedlings even though transcripts for these proteins were present. In the present study it was found that nearly all of the psaA-psaB transcripts in plastids of dark-grown plants were associated with membrane-bound polysomes. Membrane-associated polysomes from plastids of dark-grown plants synthesized the 65-70-kD chlorophyll a-apoproteins at low levels when added to a homologous in vitro translation extract capable of translation elongation. However, when etioplast membranes were disrupted with detergent, in vitro synthesis of the 65-70-kD chlorophyll a-apoproteins increased to levels observed with polysomes of plastids from illuminated plants. These results suggest that synthesis of the chlorophyll a-apoproteins of Photosystem I is arrested on membrane-bound polysomes at the level of polypeptide chain elongation. In addition to the selective activation of chlorophyll a-apoprotein translation, illumination also caused an increase in chloroplast polysomes (membrane-associated and stromal) and induced a recruitment of psbA and rbcL transcripts into chloroplast polysomes. These results indicate that in conjunction with the selective activation of chlorophyll a-apoprotein elongation, illumination also caused a general stimulation of chloroplast translation initiation.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A & M University, College Station 77843-2128.
authors.forename: R R
authors.initials: RR
authors.lastname: Klein
authors.forename: H S
authors.initials: HS
authors.lastname: Mason
authors.forename: J E
authors.initials: JE
authors.lastname: Mullet
mesh_terms: D002458:Cell Fractionation; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000502:physiology*; D005786:Gene Expression Regulation / Q000528:radiation effects; D007425:Intracellular Membranes / Q000378:metabolism; D008027:Light; D010944:Plants; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis / Q000528:radiation effects; D012333:RNA, Messenger / Q000378:metabolism; D012260:Ribonucleases / Q000037:antagonists & inhibitors; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics
chemical_list: D012333:RNA, Messenger; D002734:Chlorophyll; D012260:Ribonucleases; D012273:Ribulose-Bisphosphate Carboxylase