Characterization of Sam68-like mammalian proteins SLM-1 and SLM-2: SLM-1 is a Src substrate during mitosis

Sam68, the 68-kDa (S) under bar rC substrate associated during (m) under bar itosis, is an RNA-binding protein with signaling properties that contains a GSG ((G) under bar RP33, (S) under bar am68, (G) under bar LD-1) domain. Here we report the cloning of two (S) under bar am68-like-(m) under bar ammalian proteins. SLM-1 and SLM-2. These proteins have an approximate to 70% sequence identity with Sam68 in their GSG domain. SLM-1 and SLM-2 have the characteristic Sam68 SH2 and SH3 domain binding sites. SLM-1 is an RNA-binding protein that is tyrosine phosphorylated by Src during mitosis, SLM-1 bound the SH2 and SH3 domains of p59(fyn). Grb-2, phospholipase C gamma-1 (PLC gamma-1), and/or p120(rasGAP), suggesting if may function as a multifunctional adapter protein for Src during mitosis, SLM-2 is an RNA-binding protein that is not tyrosine phosphorylated by Src or p59(fyn). Moreover, SLM-2 did not associate with the SH3 domains of p59(fyn), Grb-2 PLC gamma-1, or p120(rasGAP), suggesting that SLM-2 may not function as an adapter protein for these proteins. The identification of SLM-1 and SLM-2 demonstrates the presence of a Sam68/SLM family whose members have the potential to link signaling pathways with RNA metabolism.