Cell-free translation of the messenger RNA for calf terminal deoxynucleotidyltransferase

Nuclear matrix bound terminal deoxynucleotidyl transferase in rat thymus nuclei. I. A possible site for TdT mediated function

Approximately 80% of the terminal deoxynucleotidyl transferase (TdT) in thymus glands from 3-4 week old rats was found to be localized in the nucleus and the remaining 20% in the cytosol. Following endogenous nuclease digestion of the thymus nuclei, 70-85% of the nuclear TdT could be removed by low salt and high salt extractions, whereas 15-30% of the enzyme remained tightly bound to the residual nuclear matrix. Low salt and high salt extracts of the nuclei contained a mixture of 58, 56, 45 and 44 kDa species of TdT whereas only 58 kDa species of the enzyme was found to be associated with the matrix. In addition to TdT, 20-25% of the nuclear DNA polymerase alpha was also tightly bound to the isolated nuclear matrix. These observations lead us to propose that besides being the site of DNA replication via-matrix bound replicational complexes [Van der Velden H.M.W. & Wanka F., Molecular Biology Reports 12 (1987): 69], nuclear matrix may also be the site of TdT mediated function and that matrix bound TdT and free TdT could be the functional and nonfunctional forms of the enzyme, respectively, in the thymus gland.

Measurement of terminal deoxynucleotidyl transferase mRNA in clinical samples: a new parameter in analysis of leukemia cells

A 1750 base pair cDNA to human terminal deoxynucleotidyl transferase (TdT) has been cloned. This cDNA detects a dominant 2200 base pair messenger RNA species in normal and leukemic cells synthesizing the enzyme. A quantitative dot blot assay was utilized to survey a number of clinical samples from patients with TdT positive and negative leukemias as well as cells from normal volunteers. A linear relationship was detected between the amount of TdT mRNA and the amount of enzyme activity in bone marrow cells. The assay is sensitive enough to detect normal TdT levels in bone marrow, and distinguish these levels from the lack of such mRNA in peripheral blood and bone marrow of patients with myeloid leukemia. Elevated levels of mRNA were found in two cases of patients in clinical remission. The prognostic significance of these observations must await further study.

Molecular biology of terminal transferase

Terminal transferase is an unusual deoxynucleotide polymerizing enzyme found only in prelymphocytes. The protein was purified to homogeneity from calf thymus glands in 1971 as a 32 kDa protein with a two peptide structure. Subsequent biochemical and immunological analyses of terminal transferase protein in crude extracts from a number of animal species showed a single peptide with a molecular weight of about 58,000. The two peptide structure found earlier was caused by proteolysis. Homogeneous 58 kDa terminal transferase has now been produced from human lymphoblastoid cells and calf thymus glands by immunoaffinity chromatography. In vitro phosphorylation studies showed that the terminal transferase protein contains one phosphorylation site near one end of the polypeptide chain, and the phosphorylation of the enzyme has been confirmed by in vivo labeling experiments. Unambiguous demonstration of the molecular weight of the human terminal transferase was obtained by translation of the cloned human terminal transferase DNA sequence to a 58,308 Da protein. The translated amino acid sequence also provided a possible phosphorylation site near the amino-terminus of the protein. Preliminary analysis of the genomic structure shows a simple intron/exon pattern with the total human terminal transferase gene spanning at least 65 Kb.