Patent ID: 7494797

Claim:
A recombinantly expressed terminal deoxynucleotidyl transferase (TdT) fusion protein comprising a truncated terminal deoxynucleotidyl transferase sequence and a protein tag sequence N-terminally fused to said truncated terminal deoxynucleotidyl transferase sequence, wherein said protein tag is selected from the group consisting of a His tag, Streptavidin binding proteins, Maltose binding proteins, GST and HA tags, and wherein the truncated terminal deoxynucleotidyl transferase sequence consists of the native calf thymus TdT sequence of SEQ ID NO: 2 N-terminally truncated by 138, 152, or 161 amino acids, wherein said recombinantly expressed terminal deoxynucleotidyl transferase fusion protein has a 20- to 30-fold higher enzyme activity in solutions containing Co2+ ions relative to solutions containing Zn/Mg ions.