FIGURE 1.

CD45 exons 4 and 5 share sequence similarity but recruit distinct proteins. A, schematic of CD45 alternative splicing, showing variable exons 4, 5, and 6 in the genomic context and the five isoforms that have been identified in human T cells. Based on antibody reactivity, isoforms encoded by mRNAs containing exon 4 are also termed RA, whereas the smallest isoform is RO. Boxes correspond to exons, and lines designate introns. B, sequence of the silencer regions of CD45 exons 4 and 5, as defined previously (Rothrock et al. (15) and Motta-Mena et al. (19)), with the ARS core element underlined and the ARS motif consensus shown above. Numbers indicate nucleotide position with respect to full exon. C, silver stain (top) and Western blot (bottom) of proteins isolated by RNA affinity using the exons 4 and 5 silencer elements (as shown in panel B), unrelated silencer sequence (NS; Melton et al. (21)), or beads alone control.