A high molecular weight form of terminal deoxynucleotidyl transferase

Abstract

CALF thymus terminal deoxynucleotidyl transferase (TdT) (EC 2.7.7.31) is a low molecular weight protein containing two peptides of MWs 24,000 and 8,000 in a native structure estimated to have a molecular weight of 32,000 (ref. 1). Use of antibody directed against homogeneous bovine transferase² for immunofluorescent cytology showed the normal thymus localisation to be cytoplasmic and nuclear, whereas bone marrow localisation is only nuclear³. Several human lymphoblastoid cell lines that contain terminal transferase activity also exhibit the nuclear location by immunofluorescence⁴. As cultured lymphoblastoid cell lines are readily labelled with radioactive amino acids we surveyed the peptides present in the immuno-precipitated transferase from these lines by fluorography of SDS gels. The results presented here show that a single 58,000-MW peptide is precipitated by monospecific rabbit antibody against bovine transferase. No peptides as small as those peptides present in calf thymus transferase were detected.