P60 IS AN ADAPTER FOR THE DROSOPHILA PHOSPHOINOSITIDE 3-KINASE, DP110

The mammalian phosphoinositide 3-kinases (PI3Ks) p110 alpha, beta, and delta form heterodimers with Src homology 2 (SH2) domain-containing a daptors such as p85 alpha or p55(PIK). The two SH2 domains of these ad aptors bind to phosphotyrosine residues (pY) found within the consensu s sequence pYXXM. Here we show that a heterodimer of the Drosophila PI 3K, Dp110, with an adaptor, p60, can be;purified from S2 cells with a pYXXM phosphopeptide affinity matrix. Using amino acid sequence from t he gel-purified protein, the gene encoding p60 was cloned and mapped t o the genomic region 21B8-C1, and the exon/intron structure was determ ined. p60 contains two SH2 domains and an inter-SH2 domain but lacks t he SH3 and breakpoint cluster region homology (BH) domains found in ma mmalian p85 alpha and beta. Analysis of the sequence of p60 shows that the amino acids responsible fbr the SH2 domain binding specificity in mammalian p85 alpha are conserved and predicts that the inter-SH2 dom ain has a coiled-coil structure. The Dp110 p60 complex was immunopreci pitated with p60-specific antisera and shown to possess both lipid and protein kinase activity. The complex was found in larvae, pupae, and adults, consistent with p60 functioning as the adaptor for Dp110 throu ghout the Drosophila life cycle.