Multivalent interactions of the SUMO-interaction motifs in RING finger protein 4 determine the specificity for chains of the SUMO.

RNF4 (RING finger protein 4) is a STUbL [SUMO (small ubiquitin-related modifier)-targeted ubiquitin ligase] controlling PML (promyelocytic leukaemia) nuclear bodies, DNA double strand break repair and other nuclear functions. In the present paper, we describe that the sequence and spacing of the SIMs (SUMO-interaction motifs) in RNF4 regulate the avidity-driven recognition of substrate proteins carrying SUMO chains of variable length.