Cloning and Characterization of the cDNA Encoding Brain Cell Membrane Protein 1 (BCMP1) Identifies a Novel Subclass of Four Transmembrane Proteins

Daniel C. Christophe
Institut de Biologie et de Médecine Moléculaires (IBMM)
IRIBHN-Faculté de Médecine, Université Libre de Bruxelles
Rue Profs. Jeener et Brachet, 12
telephone: +32-2-650 9828
fax: +32-2-650 9820
prestype: Poster
presenter: C. Christophe-Hobertus

C. Christophe-Hobertus and D. Christophe
Institut de Biologie et de Médecine Moléculaires (IBMM-IRIBHN), Université Libre de Bruxelles, B-6041 Gosselies, Belgium.

A partial cDNA sequence from dog thyroid presenting a similarity overlap with the mouse cDNA clone MNCb-0941 (GenBank acc. #: AU035837) was fortuitously isolated in the laboratory. Re-screening of a dog thyroid cDNA library resulted in the isolation of a 4kb- long cDNA exhibiting a putative open-reading frame of only 543bp followed by a 3.2kb-long 3’ untranslated region containing several ATTTA instability motifs. Bioinformatic analysis of the encoded protein sequence identified the presence of four putative transmembrane domains and of a short intracellular N-terminal domain. Similarity searches in protein and protein domains databases identified partial sequence conservations with peripheral myelin protein 22 (PMP22) and epithelial membrane proteins (EMPs), both of which belonging to the large family of four-transmembrane proteins [1]. Northern-blot analysis of the expression of the corresponding mRNA in adult dog tissues revealed the presence of a huge amount of the 4kb transcript in the brain. Lower amounts were observed in a number of other tissues, including the thyroid. The subcellular localization of the encoded protein was determined by expressing a green fluorescent protein (GFP) fusion protein in transfected COS-7 cells. A patchy fluorescence pattern was observed all over the cell surface and a strong accumulation of fluorescence in the perinuclear region was observed in most cells, which was consistent with a membranous localization of the protein.

Very recently, the complete sequence of the mouse cDNA clone MNCb-0941 was made available (GenBank acc. #: AB041540). Comparison of the encoded protein sequences with the closest members of the four-transmembrane proteins family revealed that our dog cDNA sequence and the mouse MNCb-0941 clone defined the existence of a novel subclass in this family of proteins. In view of the high level of mRNA found in the brain, we termed the protein “brain cell membrane protein 1” (BCMP1).Bioinformatic search for the sequences corresponding to human BCMP1 led to the identification of the cDNA sequence DKFZp564E153 (GenBank acc. #: AL049257) which exhibited a very high degree of sequence conservation over 2.5kb with the 3’ untranslated region of dog BCMP1 mRNA. The corresponding locus had been localized on chromosome X in man. A fragment of DNA sequence from human chromosome 8 (clone RP11-31H18 map 8, GenBank acc. #: AC041003) also presented a significant similarity with the coding region of BCMP1 mRNA. Whether this observation indicates the existence of two closely related genes in man or results from inaccurate sequence assignment in the database is currently being tested experimentally.

[1] Jetten A.M. & Suter U. (2000) Prog. Nucleic Acid Res. Mol. Biol. 64, 97-128.

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