The short splice variant of mouse terminal deoxynucleotidyl transferase (TdTS) catalyzes the addition of nontemplated nucleotides (N addition) at the coding joins of B cell and T cell antigen receptor genes. However, the activity and function of the long isoform of TdT (TdTL) have not been determined. We show here, in vitro and in vivo, that TdTL is a 3'-->5' exonuclease that catalyzes the deletion of nucleotides at coding joins. These findings suggest that the two TdT isoforms may act in concert to preserve the integrity of the variable region of antigen receptors while generating diversity.
- Alternative Splicing/*immunology Amino Acid Motifs/immunology Amino Acid Sequence Animals Antigenic Variation/*immunology B-Lymphocytes/*enzymology Cyclin-Dependent Kinase Inhibitor p21 Cyclins/chemistry DNA Nucleotidylexotransferase/genetics/*immunology Isoenzymes/genetics/immunology Mice Mice, Transgenic Molecular Sequence Data RNA/chemistry/genetics Reverse Transcriptase Polymerase Chain Reaction Sequence Homology, Amino Acid