Authors: Travesa A, Kalashnikova TI, de Bruin RA, Cass SR, Chahwan C, Lee DE, Lowndes NF, Wittenberg C.
The exquisite organization of biological processes is often determined by protein-protein interactions. Travesa et al. (p. 1476–1486) exploited the conservation of interaction interfaces to identify a novel motif that mediates the binding of two repressors, Whi5 and Nrm1, to their cognate transcription factors, SBF and MBF, respectively. Those factors, each comprising Swi6 and a DNA binding subunit, regulate gene expression at the start of the cell cycle. Interestingly, small domains from each repressor (27 to 40 amino acids) containing the conserved motif are sufficient not only to direct binding to the Swi6 carboxy terminus but also to discriminate between the two transcription factors.