A CYCLIN-DEPENDENT KINASE HOMOLOG, P130(PITSLRE), IS A PHOSPHOTYROSINE-INDEPENDENT SH2 LIGAND

Src-homology 2 (SH2) domains are conserved, globular protein modules t hat mediate assembly of multicomponent signaling complexes, Phosphopro teins from the B-lymphoid cell line A20 were isolated by SH2 affinity chromatography; the peptide sequence from one of these proteins was us ed to molecularly clone several related complementary DNAs whose predo minant protein product, p130(PITSLRE), is abundant serine/threonine ki nase with ubiquitous expression in murine tissues, The sequence of a p reviously described cyclin-dependent kinase homologue, p58(clk-1), is entirely contained within the p130(PITSLRE) sequence, Specific binding of p130(PITSLRE) to, SH2 domains is mediated by a serine- and glutami c acid-rich cluster of amino acids in the N-terminal region, This inte raction is dependent on serine/threonine phosphorylation but independe nt of tyrosine phosphorylation, Binding is inhibited by free phosphoty rosine and by a phosphotyrosine-containing peptide from polyoma middle T antigen, suggesting that the p130(PITSLRE) binding site in the SH2 domain overlaps the region that binds phosphotyrosine containing pepti des, Bacterially expressed p130(PITSLRE) fragments acquire the ability to bind an SH2 domain when phosphorylated in vitro with casein kinase II. A subset of casein kinase II phosphorylation sites may therefore constitute a phosphotyrosine-independent class of SH2 ligands.