[A method for determining the classification of a protein in a given family at a low level of similarity]

Basing on the analysis of the primary structure of proteins from a family of signal receptor proteins, the existence of short extremely conservative family-specific chains was postulated. These chains may serve as a marker in determination of the relationship of a protein to the given family. On the basis of the performed analysis, it is suggested that mass-oncogene belongs to the family of signal receptors, whereas pheromonal receptor of the yeasts STE-2--presumably does not.