Beyond the Identification of Transcribed Sequences:
Functional, Evolutionary and Expression Analysis
12th International Workshop
October 25-28, 2002
Washington, DC


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Direct Contribution of a Transposable Element to the Protein Diversity: A Novel Type Bovine Bcnt Protein that Includes the Endonuclease Domain of RTE-1

Shintaro Iwashita1, Tomohito Itoh2, Kenshiro Oshima3, Katsuyuki Hashimoto4and Wojciech Makalowski5
1Mitsubishi Kagaku Institute of Life Sciences, 2Shirakawa Institute of Animal Genetics, 3Hitachi Instruments Service Co.,Ltd., 4National Institute of Infectious Diseases, and 5Pennsylvania State University
Telephone: 81-42-724-6265
Fax: 81-42-724-6316
Email: siwast@libra.ls.m-kagaku.co.jp

Bovine p97Bcnt (after Baucentaur) is a unique molecule that includes a retrotransposable element-1 (RTE-1)-derived endonuclease domain followed by two copies of an IR module with 40-amino acids in the C-terminus. Human and mouse Bcnt proteins have no RTE-1-derived region but one IR and a highly conserved C-terminal region that is absent from bovine p97Bcnt. The chicken Bcnt gene structure suggests that the human/mouse gene is an ancestral structure and that the bovine p97Bcnt structure must represent a recent evolutionary alteration. Indeed, screening of a bovine genomic library revealed another copy of the bovine Bcnt gene whose structure resembles the ancestral gene that encodes an IR module and a highly conserved C-terminus region. Biochemical analysis showed that both h-type Bcnt and p97 Bcnt are expressed in many bovine tissues and that they are active proteins. Both genes are localized linearly on bovine chromosome 18, suggesting tandem duplication as a mechanism for the creation of the p97Bcnt gene. Consequently, one of the duplicated copies lost its 3' exons but instead recruited an RTE-1-derived endonuclease domain. In addition, an IR coding exon got duplicated and another genomic piece was exonificated to create a unique 3' part of the p97Bcnt mRNA. The phylogenetic analysis showed that the new gene is under a relaxed evolution that enables fast diversification of duplicated genes. The described evolution of the Bcnt locus enabled us to infer in detail how transposable elements contribute to the protein diversity.

References:

J. Biol. Chem. 272, 2801 (1997), Gene 211,387 (1998), BBA 1427, 408 (1999), Gene 268, 59 (2001)



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