The 5′ end of the CD5 gene indicating location of the new exon 1. (A) The human CD5 locus depicting the 5′ end of the genomic map constructed from overlapping human CD5 genomic sequence and partial genomic sequences containing exons 1, 2, and 3. The 5.3-kb human endogenous retrovirus element lies upstream of the known exon 1 sequence (E1A). Distances between the exons are indicated from exon 1 ATG (+1). The bottom panel is a gel showing whether PCR products were obtained using the sense primers indicated above each gel lane (arrowheads, the numbers refer to the oligonucleotides listed in Table 1) and CD5 E5-6 as antisense primer. Sizes are 763 bp, 811 bp, and 730 bp, respectively. (B) Cartoon depicting the proposed splice sites in E1A and E1B-type transcripts and ATG starting coding region.