Genomic sequence analysis and structure of cDNA clones representing Dβ1 germline transcripts. The genomic structure of the Dβ1 region is indicated at the top of the figure, with the area of sequence conservation (72% identity) between mouse and human indicated by the shaded box. cDNA clones representing germline TCRβ transcripts were obtained from a Rag-2^−/− thymocyte library screened with a Cβ1 probe and analyzed by DNA sequencing. Individual clones are depicted by a solid horizontal line, with the position of the 5′ end relative to the first base of Dβ1 (+1) indicated on the left. Splice junctions are indicated by circles and unsequenced regions by dashed lines.