KCNMB3 exons 1c and 1d exhibit weak conservation among mammals. (A) A segment from human KCNMB3 containing the end of shared exon 2 and exon 1c was used to search for homology among placental mammals. The translated open reading frame is shown at the top. Both exon 1c and the end of exon 2 exhibit low PhastCons scores indicative that there has been little selective pressure in this region among placental mammals. Many species also lack a triplet (CAT complementary to AUG) encoding an initiation methionine or contain gaps or inserts that disrupt the ORF (see Fig. S6 for translations of different reading frames). (B) A segment spanning the presumed human 1d exon also shows minimal conservation with other placental mammals, despite strong sequence identity in the higher primates. The intronic side of the presumed GT 5′ intron–exon splice junction is noted in the red block. The 5′ intron–exon splice site, which is conserved in primates, exhibits a number of substitutions across species, although the initial GT motif is shared among most of the displayed genomes. The presence of inserts, gaps, and missing CAT methionine-encoding triplets suggests that, other than in primates, this region may also not contribute valid ORFs in most mammals.