Identification and characterization of a mammalian protein interacting with 20S proteasome precursors

The assembly of individual mammalian proteasome subunits into catalytically active 20S proteasome is not well understood, Herein, we report the identi fication and characterization of human and mouse homologues of the yeast pr oteasome maturating factor Ump1p, We delineate the region of hUMP1 implicat ed in the specific interaction with proteasome precursors and show that hUM P1 protein is absent from the mature form of the 20S proteasome. We also sh ow that the transcript level of mammalian UMP1 is increased after IFN-gamma treatment and that mammalian UMP1 is functionally related to but not inter changeable with its yeast homologue.