We studied the regulation of three closely related members of Ras family G proteins, R-Ras,
TC21 (also known as R-Ras2), and M-Ras (R-Ras3). Guanine nucleotide exchange of R-
Ras and TC21 was promoted by RasGRF, C3G, CalDAG-GEFI, CalDAG-GEFII (RasGRP),
and CalDAG-GEFIII both in 293T cells and in vitro. By contrast, guanine nucleotide
exchange of M-Ras was promoted by the guanine nucleotide exchange factors (GEFs) for
the classical Ras (Ha-, K-, and N-), including mSos, RasGRF, CalDAG-GEFII, and CalDAG …