Phosphatidylinositol 3-kinase regulatory subunit alpha is an enzyme that in humans is encoded by the PIK3R1 gene. Phosphatidylinositol 3-kinase phosphorylates the inositol ring of phosphatidylinositol at the 3-prime position. The enzyme comprises a 110 kD catalytic subunit and a regulatory subunit of either 85, 55, or 50 kD. The Pik3r1 gene locus encodes the 85 kD regulatory subunit, as well as 55 and 50 kD regulatory subunits. It used to be thought that alternative splicing of this gene resulted in three transcript variants encoding different isoforms. In fact, it has since been shown that the 55 and 50kD subunits have their own promotors within the gene locus Pik3r1. Phosphatidylinositol 3-kinase plays an important role in the metabolic actions of insulin, and a mutation in this gene has been associated with insulin resistance. Suppression specifically of the 85kD subunit in early murine embryoid body development results in a transient cell-cell adhesion deficiency, mediated by transient downregulation of the adhesion molecule integrin-beta1 (ITGB1).