Identification and properties of terminal deoxynucleotidyltransferase from Xenopus embryos prior to the development of the thymus.

The appearance of terminal deoxynucleotidyltransferase (TdT), a marker for early lymphoid cells, has been measured during the development of the South African clawed frog, Xenopus laevis. The enzyme can first be detected in 2-day-old embryos, at approximately the same time as the first detectable embryonic immunoglobulin and well before the appearance of the thymus. Xenopus TdT has been partially purified and some of its properties have been investigated. The partially purified enzyme is 68,000 daltons in size, as measured by gel filtration, and cross-reacts immunologically with anti-calf thymus TdT.