AN AVIAN CDNA-ENCODING A TYROSINE-PHOSPHORYLATED PROTEIN WITH PDZ, COILED-COIL, AND SAM DOMAINS

Tyrosine phosphoproteins of size 115-120 kDa were purified from membra nes of chicken embryo fibroblasts (CEF) infected with Rous sarcoma vir us (RSV). A mouse was immunized with these proteins, and the immune se rum was used to screen a CEF cDNA expression library. A highly immunor eactive clone (KS5) was identified and characterized. The cDNA of this clone is 2.3 kb in length with a short 5' UTR and a single major open reading frame (ORF) encoding a polypeptide of 719 amino acids, with a calculated molecular weight of 81.1 kDa. The encoded protein contains an amino terminal PDZ domain, followed by a predicted coiled-coil reg ion, a PEST domain, and a carboxy-terminal SAM domain. Consensus seque nce motifs for tyrosine phosphorylation are also present, as are conse nsus sequences for the binding of SH2 and PDZ domains. Antisera from m ice immunized with bacterially expressed fragments of the KS5 protein recognized proteins of size 230, 116, and 65 kDa in CEF. In other chic ken embryo tissues, a 116-kDa species was the predominant protein reco gnized. The 116-kDa species is tyrosine-phosphorylated in RSV-CEF. The presence of PDZ and SAM domains in the KS5 protein suggests that it m ay act as a molecular adaptor, promoting and relaying information in a signal transduction pathway. It is a member of a family of related pr oteins, all of which have a highly conserved PDZ domain adjacent to a coiled-coil region. Two other members of this family are the neuronal proteins spinophilin (Allen, P.B., Ouimet, C.C., Greengard, P., 1997. Spinophilin, a novel protein phosphatase 1 binding protein localized t o dendritic spines. Proc. Natl. Acad. Sci. USA 94, 9956-9961) and neur abin (Nakanishi, H., Obaishi, H., Satoh, A., Wada, M., Mandai, K., Sat oh, K., Nishioka, H., Matsuura, Y., Mizoguchi, A., Takai, Y., 1997. Ne urabin: A novel neural tissue-specific actin filament-binding protein involved in neurite formation. J. Cell Biol. 139, 951-961). (C) 1998 E lsevier Science B.V. Al rights reserved.