Figure 1.

Generation of mutant mice in which the terminal deoxynucleotidyl transferase (TdT) promoter was replaced by the lck promoter. (a) Structure of the targeting vector and partial restriction map of the genomic TdT locus and mutated allele after homologous recombination. Exons 1–4 and 6 are depicted as black boxes. The location of exon 5 (white box) has not been determined. RI, EcoRI; H, HindIII; X, XbaI; S, SalI; Xh, XhoI; K, KpnI. (b) Southern blot analysis of representative mouse tail DNA. Genomic DNA was isolated from tails. DNA was digested with EcoRI and hybridized with the SalI–XbaI probe indicated. WT, wild-type littermate. (c) Expression of TdT in lckTdT^+/+ and control C57BL/6 mice. RNA prepared from each tissue was examined by Northern blot analysis using a probe of full-length cDNA of TdT. Fetal thymus RNA was prepared from embryonic day (E)14.5–E18.5 embryos. Lane 1, C57BL/6 thymus (T) at 8 weeks; lanes 2–7, lckTdT^+/+ thymuses (lane 2, E14.5; lane 3, E15.5; lane 4, E16.5; lane 5, E17.5; lane 6, E18.5; lane 7, 8 weeks). RNA from spleen (S), bone marrow (B), lymph node (L), kidney (K), brain (Br), liver (Li) and lung (Lu), was extracted from 8-week-old lckTdT^+/+ mice. 28S and 18S ribosomal bands stained with ethidium bromide are shown in the lower panel.