p60 is an adaptor for the Drosophila phosphoinositide 3-kinase, Dp110

The mammalian phosphoinositide 3-kinases (PI3Ks) p110alpha, beta, and delta form heterodimers with Src homology 2 (SH2) domain-containing adaptors such as p85alpha or p55(PIK). The two SH2 domains of these adaptors bind to phosphotyrosine residues (pY) found within the consensus sequence pYXXM. Here we show that a heterodimer of the Drosophila PI3K, Dp110, with an adaptor, p60, can be purified from S2 cells with a pYXXM phosphopeptide affinity matrix. Using amino acid sequence from the gel-purified protein, the gene encoding p60 was cloned and mapped to the genomic region 21B8-C1, and the exon/intron structure was determined. p60 contains two SH2 domains and an inter-SH2 domain but lacks the SH3 and breakpoint cluster region homology (BH) domains found in mammalian p85alpha and beta. Analysis of the sequence of p60 shows that the amino acids responsible for the SH2 domain binding specificity in mammalian p85alpha are conserved and predicts that the inter-SH2 domain has a coiled-coil structure. The Dp110.p60 complex was immunoprecipitated 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 throughout the Drosophila life cycle.