Derepression by depolymerization; structural insights into the regulation of Yan by Mae.

Yan, an ETS family transcriptional repressor, is regulated by receptor tyrosine kinase signaling via the Ras/MAPK pathway. Phosphorylation and downregulation of Yan is facilitated by a protein called Mae. Yan and Mae interact through their SAM domains. We find that repression by Yan requires the formation of a higher order structure mediated by Yan-SAM polymerization. Moreover, a crystal structure of the Yan-SAM/Mae-SAM complex shows that Mae-SAM specifically recognizes a surface on Yan-SAM that is also required for Yan-SAM polymerization. Mae-SAM binds to Yan-SAM with approximately 1000-fold higher affinity than Yan-SAM binds to itself and can effectively depolymerize Yan-SAM. Mutations on Mae that specifically disrupt its SAM domain-dependent interactions with Yan disable the derepression function of Mae in vivo. Depolymerization of Yan by Mae represents a novel mechanism of transcriptional control that sensitizes Yan for regulation by receptor tyrosine kinases.