Thymocytes from SLIP mice are defective in TCR Vβ8-Jβ2 coding joint formation. Thymocyte DNA samples were subjected to semiquantitative PCR analysis. Titrations with wild-type DNA (100, 10, 1, 0.1 ng; lanes 1–4, respectively) were performed to estimate the abundance of coding joint formation in SCID (lane 5) and two SLIP (lanes 6 and 7) DNA samples (all at 100 ng). Our primers amplify Vβ8 rearrangements to all Jβ2 members. The most prominent band in the wild-type DNA lanes is 276 bp, the expected size for Vβ8-Jβ2.6 (unrearranged DNA is not amplified). A negative PCR control (all reagents without DNA) is shown in lane 8. Relevant sizes of the DNA marker (1-kb ladder; GIBCO/BRL) are indicated adjacent to lane M.