Abstract
Tobacco chloroplast genome encodes about 80 protein genes that are expressed by chloroplast gene expression system. Many chloroplast mRNAs lack SD-like sequences, which are found in the 5'-untranslated region of most of bacterial mRNAs. A common or specific trans-acting factor is thought to be involved in translation initiation of such chloroplast mRNAs but is still obscured. We have analyzed translation initiation of chloroplast mRNAs using in vitro translation and gel shift assays. Here we show that a trans-acting factor could be shared by some chloroplast mRNAs such as atpB and psbN to facilitate translation initiation. This potential trans-acting factor preferentially bound to a U-rich region upstream of initiation codon of these mRNAs. Mechanism of translation initiation in chloroplasts will be discussed.
