Class I PI3Ks are heterodimeric molecules composed of a regulatory and a catalytic subunit; they are further divided between IA and IB subsets on sequence similarity. Class IA PI3Ks are composed of a heterodimer between a p110 catalytic subunit and a p85 regulatory subunit.[14] There are five variants of the p85 regulatory subunit, designated p85α, p55α, p50α, p85β, and p55γ. There are also three variants of the p110 catalytic subunit designated p110α, β, or δ catalytic subunit.