We used a computer-based prediction algorithm to identify probable coiled-coil segments at the N-termini of G protein alpha, beta and gamma subunits. This result indicates that G protein trimers may form via a three-stranded coiled coil. Previous biochemical results had shown that the N-termini of alpha and beta are involved in subunit interactions. Here we present a structural model for the N-terminal domain of beta gamma and a hypothesis for the reversible association of alpha to beta gamma.