A nuclear gene in maize required for the translation of the chloroplast atpB/E mRNA

To elucidate mechanisms that regulate chloroplast translation in land plant s, we sought nuclear mutations in maize that disrupt the translation of sub sets of chloroplast mRNAs. Evidence is presented for a nuclear gene whose f unction is required for the translation of the chloroplast atpB/E mRNA. A m utation in atp1 results in a failure to accumulate the chloroplast ATP synt hase complex due to reduced synthesis of the AtpB subunit. This decrease in AtpB synthesis does not result from a change in atpB mRNA structure or abu ndance. Instead, the atpB mRNA is associated with abnormally few ribosomes in atp1-1 mutants, indicating that atp1 function is required during transla tion initiation or early in elongation. Previously, only one nuclear gene t hat is required for the translation of specific chloroplast mRNAs had been identified in a land plant. Thus, atp1 will be a useful tool for dissecting mechanisms of translational control in chloroplasts.