Chloroplast RNA-binding and pentatricopeptide repeat proteins.
Chloroplast gene expression is mainly regulated at the post-transcriptional level by numerous nuclear-encoded RNA-binding protein factors. In the present study, we focus on two RNA-binding proteins: cpRNP (chloroplast ribonucleoprotein) and PPR (pentatricopeptide repeat) protein. These are suggested to be major contributors to chloroplast RNA metabolism. Tobacco cpRNPs are composed of five different proteins containing two RNA-recognition motifs and an acidic N-terminal domain. The cpRNPs are abundant proteins and form heterogeneous complexes with most ribosome-free mRNAs and the precursors of tRNAs in the stroma. The complexes could function as platforms for various RNA-processing events in chloroplasts. It has been demonstrated that cpRNPs contribute to RNA stabilization, 3'-end formation and editing. The PPR proteins occur as a superfamily only in the higher plant species. They are predicted to be involved in RNA/DNA metabolism in chloroplasts or mitochondria. Nuclear-encoded HCF152 is a chloroplast-localized protein that usually has 12 PPR motifs. The null mutant of Arabidopsis, hcf152, is impaired in the 5'-end processing and splicing of petB transcripts. HCF152 binds the petB exon-intron junctions with high affinity. The number of PPR motifs controls its affinity and specificity for RNA. It has been suggested that each of the highly variable PPR proteins is a gene-specific regulator of plant organellar RNA metabolism.
Center for Gene Research, Nagoya University, Nagoya 464-8602, Japan.
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T
Nakamura
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G
Schuster
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Sugiura
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Sugita
D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D002736:Chloroplasts / Q000378:metabolism*; D015870:Gene Expression / Q000502:physiology; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D020449:Repetitive Sequences, Amino Acid
D029681:Arabidopsis Proteins; C477515:HCF152 protein, Arabidopsis; D016601:RNA-Binding Proteins