Src: more than the sum of its parts.

The Src family of protooncoproteins is required for prc through at least two phases of the cell cycle and for sc cell-type-specific functions. Recent crystal structures of fragments of two representatives reveal a compact am their Src-homology 3 (SH3), SH2 and catalytic domai embodies an unexpected mechanism of regulation. Th. the enzymatic activity of Src is controlled by intramol associations between the SH2 domain and C-tail and SH3 domain and a surprising internal target. The stn highlight a mechanism by which substrates can comp internal sequences for binding to the SH3 and SH2 do thereby stimulating kinase activity. This implies that distinction between upstream activators and downstre will sometimes be ambiguous.