There are five variants of the PI3K regulatory subunit, designated p85alpha, p55alpha, p50alpha, p85beta and p55gamma (there are also three variants of the p110 catalytic subunit designated p110alpha, beta, or delta). The first three regulatory subunits are all splice variants of PIK3R1 (p85 or regulatory subunit alpha), the other two are expressed by PIK3R2 and PIK3R3, known as p85 beta, and p55 gamma, respectively. The most highly expressed regulatory subunit is p85alpha. The 3 variants forms of p85 alpha are not explicitly represented in this set.