Exon trapping was used to identify portions of genes on human chromoso
me 21. BLAST search of databases revealed that the trapped sequence hm
c02a08 (one of 559 different trapped exons) was identical to a region
of GenBank entry U61166 for an SH3 (Src-homology) domain-containing ge
ne SH3D1A (formerly called SH3P17; Sparks et al., 1996). We subsequent
ly mapped this gene to YACs and cosmids within 21q22.1-->q22.2 between
DNA markers D21S319 and D21S65 using hybridization and PCR amplificat
ion.