A NOVEL 205-KILODALTON TESTIS-SPECIFIC SERINE THREONINE PROTEIN-KINASE ASSOCIATED WITH MICROTUBULES OF THE SPERMATID MANCHETTE

To identify proteins which interact with and potentially modulate the function of microtubules during spermatogenesis, we prepared a total t estis MAP (microtubule-associated protein) antiserum and used it to is olate cDNA clones from a mouse testis cDNA expression library. Antibod ies affinity purified by using one expression clone recognized a 205-k Da protein, termed MAST205, which colocalizes with the spermatid manch ette. Sequencing of full-length cDNA clones encoding MAST205 revealed it to be a novel serine/threonine kinase with a catalytic domain relat ed to those of the A and C families. The testis-specific MAST205 RNA i ncreases in abundance during prepuberal testis development, peaking at the spermatid stage. The microtubule-binding region of MAST205 occupi es a central region of the molecule including the kinase domain and se quences C terminal to this domain. Binding of MAST205 to microtubules requires interaction with other MAPs, since it does not bind to MAP-fr ee tubulin. A 75-kDa protein associated with immunoprecipitates of MAS T205 from extracts of both whole testis and testis microtubules become s phosphorylated in in vitro kinase assays. This 75-kDa substrate of t he MAST205 kinase may form part of the MAST205 protein complex which b inds microtubules. The MAST205 protein complex may function to link th e signal transduction pathway with the organization of manchette micro tubules.