Complete sequence of the ovine β-casein-encoding gene and interspecies comparison

The 9149-bp transcription unit encoding ovine β-casein (Cas) and 4636 bp of 5′ flanking region were completely sequenced. The gene is composed of nine exons and its overall organization is similar to that of its counterparts from other species. Intron 4, the largest, shares three similar stretches (sizes ranging from 0.1 to 0.3 kb) with the region upstream from the transcription unit. These common sequences are part of short interspersed nuclear elements (SINE) specific to Bovidae (Bov). Intron 4 contains two 274-bp Bov-A2 SINE in opposite orientation, as well as a full-length 569-bp Bov-B SINE. This latter SINE, also present in caprine intron 4, is missing in cattle. This suggests that the amplification of Bov- SINE has continued after the divergence of cattle from sheep and goats, assuming that the presently known sequences are representative of these species.