Characterisation of a second, apparently inactive, copy of the bovine beta-lactoglobulin gene

A bovine cosmid clone was isolated which contains the previously characterised beta-lactoglobulin gene and, in addition, a related sequence which appears to be a beta-lactoglobulin pseudogene. The total length of the pseudogene, as determined by DNA sequencing, is 4.8 kb, similar to that of beta-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 beta-lactoglobulin sequence. It is suggested that this is the result of a recent gene conversion event involving conversion of the pseudogene by the authentic beta-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 beta-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.