Any member of a family of monomeric G proteins, with molecular mass typically \(\pu{20\!{-}\! 40 kDa}\), that also bind guanine nucleotides and are involved in signal transduction.
Source: PAC, 2012, 84, 1113. (IUPAC glossary of terms used in immunotoxicology (IUPAC Recommendations 2012)) on page 1245 [Terms] [Paper]