A novel N-terminal domain directs membrane localization of mouse testis-specific calpastatin.
Multiple isoforms of calpastatin have been identified with unique N-terminal regions followed by identical calpain inhibitory domains (II-IV). In many instances the isoforms are cell-type specific, although the precise functional differences among these N-terminal regions are largely unknown. Here we report a germ cell-specific isoform of calpastatin (tCAST) that consists of a novel N-terminal peptide of 40 amino acids (domain T) followed by domains II to IV of somatic calpastatin (sCAST). Domain T is responsible for membrane association of tCAST through a protein modification by myristylation. Mutation of the myristylation site eliminates membrane targeting. Unlike most of the isoforms of calpastatin that are generated through alternative RNA splicing or post-translational proteolysis, the testis-specific isoform is transcribed from an intronic promoter in haploid germ cells of the testis. The intronic promoter directs specific expression of a reporter transgene in developing germ cells of the mouse testis.
Li
S
S
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208, USA.
Goldberg
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E
D000818:Animals; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005854:Germ Cells / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D017403:In Situ Hybridization; D008297:Male; D021962:Membrane Microdomains / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D019814:Myristic Acid / Q000737:chemistry; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis / Q000302:isolation & purification; D013347:Subcellular Fractions / Q000378:metabolism; D013737:Testis / Q000201:enzymology*; D014162:Transfection
D002135:Calcium-Binding Proteins; D012333:RNA, Messenger; D019814:Myristic Acid; C033668:calpastatin