Translation initiation sites and relative activity of large and small forms of human choline acetyltransferase.

We have previously shown that translation of human choline acetyltransferase (ChAT) mRNA starts at least at two sites and produces two enzyme proteins with different molecular weights. In this study, translation initiation sites and relative activity of large and small forms of ChAT were determined by site-directed mutagenesis, followed by expression and immunoblotting analyses. The large and small forms were translated at the first and second ATG codons of ChAT cDNA, respectively, and the specific activity was almost the same between the two forms of the enzyme.