This is a repeated domain found in de-ubiquitinating proteins. It's exact function is not known although it is likely to be involved in the binding of the Ubps in the complex with Rsp5 and Rup1.

1: A global census of fission yeast deubiquitinating enzyme localization and interaction networks reveals distinct compartmentalization profiles and overlapping functions in endocytosis and polarity. Kouranti I, McLean JR, Feoktistova A, Liang P, Johnson AE, Roberts-Galbraith RH, Gould KL; PLoS Biol. 2010; [Epub ahead of print] PMID:20838651

2: Hse1, a component of the yeast Hrs-STAM ubiquitin-sorting complex, associates with ubiquitin peptidases and a ligase to control sorting efficiency into multivesicular bodies. Ren J, Kee Y, Huibregtse JM, Piper RC; Mol Biol Cell. 2007;18:324-335. PMID:17079730