Southern blot showing Ig heavy-chain rearrangement in splenic DNA of Tat-transgenic mice. DNA was extracted from spleens of two independent lines of Tat-transgenic mice, 24 and 29. The DNA was digested with EcoRI for IgJ heavy-chain analysis orHpaI for TCR-β analysis, blotted, and hybridized with an (A) IgJ heavy-chain probe or (B) TCR-β probe. C, control mouse; T, Tat-transgenic mouse. C1-C3 and T1-T3 refer to individual control and transgenic mice. Transgenic lines from which the mice were derived are indicated above the blots. The sizes of the bands in kilobase are indicated on the left. The 2.2-kb, 2.5-kb, and 3.1-kb bands in the Tat-transgenic samples indicate a J_H rearrangement; there was no apparent rearrangement of the TCR-β gene.