Understanding protein-protein interactions by genetic suppression

Protein-protein interactions influence many cellular processes and it is in creasingly being felt that even a weak and remote interplay between two sub units of a protein or between two proteins in a complex may govern the fate of a particular biochemical pathway. In a bacterial system where the compl ete genome sequence is available, it is an arduous task to assign function to a large number of proteins. It is possible that many of them are periphe rally associated with a cellular event and it is very difficult to probe su ch interaction. However, mutations in the genes that encode such proteins ( primary mutations) are useful in these studies. Isolation of a suppressor o r a second-site mutation that restores the phenotype abolished by the prima ry mutation could be an elegant yet simple way to follow a set of interacti ng proteins. Such a reversion site need not necessarily be geometrically cl ose to the primary mutation site.