NEW ACTIVATED RAS2 MUTATIONS IDENTIFIED IN SACCHAROMYCES-CEREVISIAE

Activating mutations in RAS proto-oncogenes encode proteins with great er GTP binding. Such mutant proteins are responsible for many human ca ncers. Six new amino acids were discovered that can yield an activated Saccharomyces cerevisiae RAS2 protein when they are altered. These ne w RAS2 alleles were found among a collection of 35 random mutations th at exhibit a dominant reduction of glycogen accumulation. The RAS2-P41 S and RAS2-E99K alleles encode proteins that have lost responsiveness to GTPase activating proteins. They affect amino acids in loop 2 and h elix 3 respectively and illustrate that GTPase activating proteins rec ognize a larger portion of the RAS structure than previously realized. RAS2 mutations E130K, S153F, A154T, and A157S alter amino acids proxi mal to the guanine binding site and probably influence nucleotide bind ing either directly or indirectly.