EXISTENCE OF A BOVINE LINE REPETITIVE INSERT THAT APPEARS IN THE CDNAOF BOVINE PROTEIN BCNT IN RUMINANT, BUT NOT IN HUMAN, GENOMES

A novel protein, BCNT, originally isolated from bovine brain and named after Bucentaur, contains an internal portion that is translated from part of bovine LINE repetitive sequence (Bov-B LINE). Human cDNA high ly homologous to the bovine bent (bbcnt) cDNA has been isolated but do es not contain a sequence similar to the Bov-B LINE insert (Nobukuni, T., Kobayashi, M., Omori, A., Ichinose, S., Iwanaga, T., Takahashi, I. , Hashimoto, K., Hattori, S., Kaibuchi, K., Miyata, Y., Masui, T., Iwa shita, S., 1997. An Alu-linked repetitive sequence corresponding to 28 0 amino acids is expressed in a novel bovine protein, but not in its h uman homologue. J. Biol. Chem. 272, 2801-2807). In this study, we cond ucted a polymerase chain reaction analysis to investigate whether such a Bov-B LINE insert is present in bent orthologs in other animals and in the genomic sequence of the human BCNT (hBCNT) gene. The results i ndicate that the Bov-B LINE insert is present in the genomic sequences of bent orthologs from sheep, goats, axis deer, and mouse deer (chevr otain), that is in Ruminantia, but not in pigs or human. Analysis of t he bbcnt genomic sequence around the Bov-B LINE insert revealed a larg e part of the inserted Bov-B LINE sequence to be included in an exon; this is followed by a 54-nucleotide sequence that is highly homologous to Bov-B LINE in the 3'-side intron. The hBCNT gene was isolated and found to consist of seven exons and six introns, among which the intro n corresponding to the Bov-B LINE insertion site in the bbcnt genome i s 16.5 kb in length with no sequence similar to Bov-B LINE. Based on t hese results, it seems likely that the Bov-B LINE insert is derived fr om a long Bov-B LINE repetitive sequence transposed to an ancestral be nt gene in Ruminantia and reformed as a new exon through new splicing sites in the transposed sequence. (C) 1998 Elsevier Science B.V. All r ights reserved.