Regional homology in GTP-binding proto-oncogene products and elongation factors.

The mammalian ras proteins and the bacterial elongation factors share the ability to interact with guanine nucleotides. Comparison of the amino acid sequences has revealed the presence of multiple homologous regions common to all members of the ras and elongation factor families. Two homologous regions share sequence similarities and predicted secondary structure with areas of the elongation factors which have been implicated in GTP binding, suggesting that these regions are part of a common GTP-binding domain. Two other homologous regions contain critical amino acids for the activation of the transforming potential of the mammalian ras proteins. The predicted secondary structure containing residue 61, but not 12, is the same for the ras proteins and elongation factors. It is proposed that the aligned homologous regions surrounding position 12 constitute common functional binding sites with different specificities; by analogy to other GTP-binding proteins, a likely candidate to interact at such a site is a GTPase-subunit.