Characterisation of a Second, Apparently Inactive, Copy of the Bovine β‐lactoglobulin Gene

A bovine cosmid clone was isolated which contains the previously characterised β‐lactoglobulin gene and, in addition, a related sequence which appears to be a β‐lactoglobulin pseudogene. The total length of the pseudogene, as determined by DNA sequencing, is 4.8 kb, similar to that of β‐lactoglobulin. Both genes are in the same orientation and are separated by approximately 14 kb intergenic sequence. Although most of introns I‐V are extremely divergent, the exon sequences are clearly related, exons I‐V exhibiting nucleotide sequence similarities in the range 60–87%. Exons VI and VII, together with the final intron, comprise a region of sequence extending over 730 bp, which displays 92.5% identity to the corresponding β‐lactoglobulin sequence. It is suggested that this is the result of a recent gene conversion event involving conversion of the pseudogene by the authentic β‐lactoglobulin gene. Identification of the new lactoglobulin sequence as a pseudogene is based on the occurrence of a stop codon in exon V. Comparison of the inferred translation product encoded by the pseudogene before its mutational inactivation, with the sequences of equine and feline β‐lactoglobulins I and II, indicates that the bovine pseudogene is more closely related to these type‐II lactoglobulin sequences than to the type‐I sequences.