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 membranes of chicken embryo fibroblasts (CEF) infected with Rous sarcoma virus (RSV). A mouse was immunized with these proteins, and the immune serum was used to screen a CEF cDNA expression library. A highly immunoreactive 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 region, a PEST domain, and a carboxy-terminal SAM domain. Consensus sequence motifs for tyrosine phosphorylation are also present, as are consensus sequences for the binding of SH2 and PDZ domains. Antisera from mice immunized with bacterially expressed fragments of the KS5 protein recognized proteins of size 230, 116, and 65 kDa in CEF. In other chicken embryo tissues, a 116-kDa species was the predominant protein recognized. The 116-kDa species is tyrosine-phosphorylated in RSV-CEF. The presence of PDZ and SAM domains in the KS5 protein suggests that it may act as a molecular adaptor, promoting and relaying information in a signal transduction pathway. It is a member of a family of related proteins, 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 to dendritic spines. Proc. Natl. Acad. Sci. USA 94, 9956-9961) and neurabin (Nakanishi, H., Obaishi, H., Satoh, A., Wada, M., Mandai, K., Satoh, K., Nishioka, H., Matsuura, Y., Mizoguchi, A. , Takai, Y., 1997. Neurabin: A novel neural tissue-specific actin filament-binding protein involved in neurite formation. J. Cell Biol. 139, 951-961).