THE HUMAN CHOLINE-ACETYLTRANSFERASE GENE ENCODES 2 PROTEINS

Both 2,500- and 6,000-nucleotide (nt) mRNAs are generated by alternati ve splicing of the primary transcript from the human gene for choline acetyltransferase (ChAT), the 68-kDa enzyme that synthesizes acetylcho line. In vitro translation of cRNA derived from a clone of the 2,500-n t mRNA produced a protein with ChAT activity demonstrating that this t ranscript encodes the human ChAT enzyme. An antibody directed against a unique amino acid sequence predicted from the 6,000-nt ChAT gene tra nscript identified a 27-kDa protein on immunoblots of human nucleus ba salis proteins. This protein was further shown to cross-react with ant ibodies prepared against the 68-kDa human ChAT enzyme. Gel-filtration chromatography of human nucleus basalis proteins demonstrated that the 27-kDa protein does not have ChAT activity, which eluted as a single peak coincident with that of the 68-kDa enzyme. The 27-kDa protein was , however, shown to colocalize with the ChAT enzyme in cholinergic neu rons of the human spinal cord using immunohistochemical techniques.