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

To elucidate mechanisms that regulate chloroplast translation in land plants, we sought nuclear mutations in maize that disrupt the translation of subsets of chloroplast mRNAs. Evidence is presented for a nuclear gene whose function is required for the translation of the chloroplast atpB/E mRNA. A mutation in atp1 results in a failure to accumulate the chloroplast ATP synthase 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 abundance. Instead, the atpB mRNA is associated with abnormally few ribosomes in atp1-1 mutants, indicating that atp1 function is required during translation initiation or early in elongation. Previously, only one nuclear gene that 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.