Alternative 5′ exons of the 4.1R gene.

(A) Sequence comparison of human versus mouse alternative 4.1R 5′ exons. The orthologous exons had the following sequence identities: 1A, 72% over a region of 142 nt; 1B, 79% over 107 nt; and 1C, 83% over 159 nt. Origins of sequences: for exon 1A, mouse sequence was from AA014918, and human from M61733 and BG943340. For exon 1B, mouse sequence was from L00919, while the human sequence was deduced by comparing the mouse 1B sequence to human genomic sequence downstream of exon 1A. That the predicted human 1B can splice to exon 2 was confirmed by RT-PCR analysis (Figure 3). For exon 1C, human sequence was from AL041809, while mouse sequence was derived from a 5′ RACE product from mouse spleen (results not shown). (B) Structure of the 5′ region of the 4.1R gene. The genomic map was constructed from overlapping BAC human genomic clones derived from high-throughput genomic sequences. Distances between exons (in kilobases) are indicated, and the location of CpG islands is shown. (C) Model showing independent splicing of alternative 5′ exons to downstream exon 2, to generate 3 4.1R transcript classes with different 5′ end sequences.