CHARACTERIZATION OF A 2ND MEMBER OF THE SENTRIN FAMILY OF UBIQUITIN-LIKE PROTEINS

Sentrin is a novel ubiquitin-like protein that can be conjugated to ot her proteins in a manner analogous to ubiquitination, Two additional c DNA sequences that encode proteins highly homologous to sentrin have b een reported to GenBank(TM), It is not known whether these sentrin-lik e proteins could also function as protein modifiers. In this report, a second member of the sentrin family was characterized in detail. Sent rin-2 is a 95-amino acid polypeptide that is 46% identical and 66% hom ologous to sentrin-1. Northern blot analysis showed that the sentrin-2 message was expressed in all tissues, but was barely detectable in th e liver and placenta. The ability of sentrin-2 to conjugate to other p roteins was tested by expressing hemagglutinin epitope-tagged sentrin- 2 in COS cells. Western blot analysis showed that sentrin-2 could be t ransferred to other proteins in a pattern similar to that of sentrin-1 conjugation and had similar C-terminal processing. We further showed that both sentrin-1 and sentrin-2 could covalently modify RanGAP1, a R an GTPase-activating protein critically involved in nuclear transport. Immunocytochemical analysis showed that sentrin-2 derivatives were hi ghly enriched in the nucleus. Taken together, our results demonstrate that sentrin-2 is another protein modifier for the sentrinization path way.