ABSTRACT
This chapter reviews the highlights of the historical development of knowledge of the biochemistry and biology of terminal deoxynucleotidyl transferase (TdT). It discusses promising new approaches to the puzzle of TdT function. The absolute level of TdT activity in thymus varies from species to species, a finding which may be related to thymic development in the particular species under study. Studies of single cells as well as fractionation of bone marrow cell populations designed to enrich for TdT containing cells, confirmed the organ location. In the neoplastic counterparts of most normal cells which contain TdT, very high levels of the enzyme are expressed. Use of immunospecific reagents for TdT coupled with fluorescence or peroxidase detection has provided a wealth of information concerning the intracellular compartmentalization of TdT. The calf thymus gland is rich in TdT activity and the tissue is relatively easy to obtain in large quantity.
