The formation of specIfIc protem-protein interactions IS one of the key mechamsms for signal transduction medIated by tyrosme phosphorylation.
These intermolecular mteractIons target signaling proteins to particular cellu-
lar locatIons and modulate the enzymatIc actIvItIes that further propagate the
sIgnal. A dIstmctIve characteristIc of the pathways that are mItIated by tyrosme
phosphorylation is that target recognition and catalytic activity are usually
functions of separate domams wIthin the signaling molecules that participate
m these pathways. Each of the sIgnalIng molecules contains one or more of a
set of modular peptide-bmdmg domains that are responsible for generating
protein-protem interactions. Such peptide-recognition domains are modular in
both structural and functIOnal respects: They are capable of folding correctly
when removed from the parent protein, and they can usually recognize their
targets even when isolated.