Abstract
During early chloroplast differentiation, regulation of plastid genetic system is known to be greatly different from that in the mature chloroplast, suggesting the existence of regulation factors specifically function at this stage. We have characterized NUS1 protein of rice, a novel chloroplast-localized RNA-binding protein. NUS1 protein accumulated abundantly in the pre-emerged immature leaf whereas it disappeared in the mature leaf. NUS1 has a molecular weight of 30 kDa, and the BN-PAGE analyses demonstrated that NUS1 was involved in the ~100kDa protein complex. C-terminus region of NUS1 showed structural similarity to an E. coli RNA-binding protein. Mobility gel shift assays indicated that NUS1 protein bound to some regions of chloroplast RNA involving the 5' precursor region of chloroplast 16S rRNA. NUS1-deficient mutant showed severe leaf chlorosis at low temperature. In the chlorotic leaves of the mutant seedling, maturation of chloroplast rRNA was impaired and the chloroplast translation/transcription capacity was severely suppressed, suggesting that NUS1 has important roles in the regulation of chloroplast genetic system during early leaf development in rice.
