PROTEIN-BINDING AND SIGNALING PROPERTIES OF RIN1 SUGGEST A UNIQUE EFFECTOR FUNCTION

wHuman RIN1 was first characterized as a RAS binding protein based on the properties of its carboxyl-terminal domain, We now show that full- length RIN1 interacts with activated RAS in mammalian cells and define s a minimum region of 434 aa required for efficient RAS binding, RIN1 interacts with the ''effector domain'' of RAS and employs some RAS det erminants that are common to, and others that are distinct from, those required for the binding of RAF1, a known RAS effector, The same doma in of RIN1 that binds RAS also interacts with 14-3-3 proteins, extendi ng the similarity between RIN1 and other RAS effecters, When expressed in mammalian cells, the RAS binding domain of RIN1 can act as a domin ant negative signal transduction blocker, The amino-terminal domain of RIN1 contains a proline-rich sequence similar to consensus Src homolo gy 3 (SH3) binding regions, This RIN1 sequence shows preferential bind ing to the ABL-SH3 domain in vitro. Moreover, the amino-terminal domai n of RIN1 directly associates with, and is tyrosine phosphorylated by, c-ABL, In addition, RIN1 encodes a functional SH2 domain that has the potential to activate downstream signals, These data suggest that RIN 1 is able to mediate multiple signals, A differential pattern of expre ssion and alternate splicing indicate several levels of RIN1 regulatio n.