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

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Abstract
Sam68, the 68-kDa Src substrate associated during mitosis, is an RNA-binding protein with signaling properties that contains a GSG (GRP33, Sam68, GLD-1) domain. Here we report the cloning of two Sam68-like-mammalian proteins, SLM-1 and SLM-2. These proteins have an ≈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 p59fyn, Grb-2, phospholipase Cγ-1 (PLCγ-1), and/or p120rasGAP, suggesting it 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 p59fyn. Moreover, SLM-2 did not associate with the SH3 domains of p59fyn, Grb-2, PLCγ-1, or p120rasGAP, 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.