Terminal deoxynucleotidyltransferase. Alignment of alpha- and beta-subunits of the core enzyme along the primary translation product

Abstract

Terminal deoxynucleotidyltransferase exists in multiple Mr forms, all apparently generated from a single polypeptide of 62kDa. On isolation and purification, the smallest catalytically active protein of this enzyme consists of two subunits, alpha (12kDa) and beta (30kDa). Recently a complementary-DNA nucleotide sequence has been reported for a portion of the enzyme from human lymphoblast. We have pinpointed the locations of the alpha- and beta-subunits within the elucidated nucleotide sequence. From these data, the portions of the nucleotide sequence coding for the catalytically important area of the transferase can be estimated. Here the amino acid sequence of a number of tryptic peptides from calf alpha- and beta-subunits is presented. Because of the striking homology between the amino acid sequence of the calf enzyme and that predicted for human lymphoblast enzyme, it is possible for us to conclude that the alpha-subunit was generated from the C-terminus of the precursor protein and the beta-subunit was non-overlapping and proximal.