Characterization of the CSNIAG allele of the bovine αs1-casein locus by the insertion of a relict of a long interspersed element

The bovine CSN1AG allele is associated with a lower proportion of as1-casein in milk and is characterized by an insertion in the last noncoding exon (19th). According to DNA sequence analysis, the location, length, and origin of the insertion characterizing the bovine CSN1AG allele have been identified. This insertion interrupts the 19th exon between nucleotides 58 and 59, is 371 bp long, and has a high level of homology with relicts of long interspersed elements of retropositional origin. Northern blot analysis shows that the inserted element is transcribed and that the number of transcripts of the CSN1AG allele is less than one-half of the number of transcripts of the CSN1AB allele. The lower amount of as1-casein in milk obtained from cows carrying the CSN1AG allele can be explained by a reduced mRNA stability. Furthermore, a method has been developed using polymerase chain reaction for identification of the carriers of the CSN1AG allele.