Drosophila choline acetyltransferase uses a non-AUG initiation codon and full length RNA is inefficiently translated

RNA from a partial cDNA clone containing the entire protein coding sequence of Drosophila melanogaster acetyl-CoA:choline O-acetyltransferase (EC 2.3.1.6; choline acetyltransferase) can be translated into active enzyme. This is unusual since this partial cDNA clone contains no appropriate ATG (AUG) initiation codon. In this study we use in vitro deletion and point mutants to identify GTG as the starting codon for protein translation. We also report the sequence of a full length Drosophila choline acetyltransferase cDNA and demonstrate that RNA produced by this clone is translated into active choline acetyltransferase but at a significantly reduced efficiency when compared to the partial cDNA clone. These results indicate that translational control may be an important regulatory step in production of Drosophila choline acetyltransferase.