Since alternatively spliced exons often contain ESEs for binding of splicing regulators that determine the fate of the exon (exon inclusion or exclusion), we wondered whether ESEs for binding of splicing regulatory proteins existed in exon 2 of CD200. For this purpose, both RESCUE-ESE (34) and ESEfinder (35) were used to search for ESEs in the exon 2 of CD200. Only one ESE was identified in exon 2 by both RESCUE-ESE and ESEfinder. The ESE existed in exon 2 of CD200 in human, mouse and rat, with the sequence TCAGGA ( Figure 2A ). The identified ESE represents a known binding site for a splicing regulatory protein SF2/ASF, a member of the SR protein family (35) .