AFAP-120 - A VARIANT FORM OF THE SRC SH2 SH3-BINDING PARTNER AFAP-110IS DETECTED IN BRAIN AND CONTAINS A NOVEL INTERNAL SEQUENCE WHICH BINDS TO A 67-KDA PROTEIN/

SH2 and SH3 domains have been characterized as functional domains that mediate protein-protein interactions in signal transduction. Recently , the cDNA sequence of a novel Src- and Fyn-binding protein called AFA P-110, for Actin-Filament Associated Protein-110 kDa, was reported. Th is protein was distinctive in that it is both an SH2 and SH3 binding p artner for the nonreceptor tyrosine kinases Src and Fyn. Here, we repo rt the characterization of an alternatively processed form of AFAP-110 that encodes an additional 258 base pair (bp) Of Open reading frame. Transient expression of this full-length clone reveals a molecular mas s of 120 kDa. Western blot analysis indicate that a larger 120-kDa var iant of AFAP-110 can be detected in brain and is not detectable in any other tissues examined. Northern blot analysis indicate that the nove l 258-bp insert can be detected in brain RNA but not chick embryo fibr oblast RNA. We propose the name AFAP-120, for Actin Filament-Associate d Protein-120 kDa. Expression of the 258-bp novel insert (NINS) as a g lutathione S-transferase encoded fusion protein permits adsorption of a 67kDa protein from tissue lysates. Deletion analysis of the NINS ind icates that the interaction with p67 can be attributed to a proline-ri ch motif that resembles an SH3-binding motif. We hypothesize that AFAP -1S0 facilitates interactions in brain between SH2/SH3 signaling prote ins and actin filaments and that a proline-rich motif in the NINS may exist to facilitate additional interactions between cellular proteins in brain and actin filaments.