A heterodimeric protein complex that possesses 1-phosphatidylinositol-4-phosphate 3-kinase activity; comprises a catalytic Class IA phosphoinositide 3-kinase (PI3K) subunit of 110-120 kDa and an associated SH2 domain-containing regulatory subunit that is a member of a family of related proteins often called p85 proteins. Class I PI3Ks phosphorylate phosphatidylinositol [PI], phosphatidylinositol-4-phosphate [PI(4)P] and phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], and are divided into subclasses A and B according to the type of adaptor subunit with which they associate. Through the interaction with the SH2-containing adaptor subunits, Class IA PI3K catalytic subunits are linked to tyrosine kinase signaling pathways.