ABSTRACT
Since the discovery of the implications of the family of ras genes in human malignancy, several families of small monomeric GTPases have been identified with a molecular mass of 20 to 25 kDa. Almost 100 distinct proteins of this superfamily have now been characterized. Based on the degree of conservation of their respective primary sequences, different families have been defined and grouped into three major branches. Although for most of these proteins little more than their primary structure is known, this provisional assignment may provide some light into the understanding of their biological functions.
