Translational Regulation of Chloroplast Genes

Abstract

We have examined the effects of illumination, carbon source, and levels of chloroplast protein synthesis on trans-acting proteins that bind to the leaders of five representative chloroplast mRNAs. The accumulation of these five chloroplast mRNAs and the proteins they encode were measured in cells grown under identical conditions. Extracts from all cell types examined contain a minimum set of six chloroplast 5-untranslated region (UTR)-binding proteins (81, 62, 56, 47, 38, and 15 kDa). Fractionation results suggest that multiple forms of the 81-, 62-, and 47-kDa proteins may exist. A 36-kDa protein was found in all cells except those deficient in chloroplast protein synthesis. Binding of the 81-, 47-, and 38-kDa proteins to the rps12 leader is effectively competed by the atpB or rbcL 5-UTRs, indicating that the same proteins bind to all three leaders. In contrast, these three proteins do not bind to the nuclear-encoded ␣-1 tubulin leader, which bound novel proteins of 110, 70, and 43 kDa. Cis-acting sequences within the 5-UTRs of two chloroplast mRNAs (rps7 and atpB) have been identified which are protected from digestion by RNase T1 by extracts enriched for the 81-, 47-, and 38-kDa proteins.

Molecular cloning of the maize gene crp1 reveals similarity between regulators of mitochondrial and chloroplast gene expression

“…RNA-binding proteins detected with in vitro binding assays have also been proposed to modulate chloroplast translation (Danon and Mayfield, 1991;Zerges and Rochaix, 1994;Hauser et al, 1996;Hirose and Sugiura, 1996). However, results presented here provide the first sequence and biochemical analysis of a protein with a genetically defined role in chloroplast translation.…”

Translational Regulation in the Chloroplast

“…This requires the determination of the significance of each protein to translational regulation. The leve1 of the 36-kD protein was diminished in cells that preferentially translate chloroplast-encoded ribosomal proteins, suggesting that it may be required for translation of a class of mRNAs encoding photosynthetic proteins (Hauser et al, 1996). Binding of a 46-kD protein to the 5'-UTR of psbC was detected only in cells carrying the nuclear mutation F64, which is responsible for the translational arrest of the chloroplast psbC mRNA.…”

“…Comparisons of 5'-UTR interacting proteins of rps22, rbcL, and atpB have detected at least seven binding proteins of 15,36,38,47,56,62, and 81 kD. The 38-, 47-, and 81-kD proteins were shown to associate with a11 tested 5'-UTRs, and multiple forms of the 47-and 81-kD proteins have been identified (Hauser et al, 1996). These results, obtained by W cross-linking, which mostly detects proteins that have direct contact with the RNA, show that several proteins may associate with the 5'-UTR of chloroplast mRNAs.…”

Small cis-Acting Sequences That Specify Secondary Structures in a Chloroplast mRNA Are Essential for RNA Stability and Translation

“…In several cases, these factors have been shown to be required for the expression of a single chloroplast gene, acting through the 5Ј untranslated region (UTR) (19,54,71). Biochemical studies have identified RNAbinding proteins that associate with 5Ј UTRs in vitro, and these proteins have been proposed to have roles in gene expression (17,30,39,72). In general, these RNA-binding proteins do not appear to be sequence specific, and their roles in chloroplast gene expression remain to be confirmed.…”