14-814 Sigma-AldrichUbcH8 Conjugating Enzyme, 100 µg

Ubiquitin-(Ub) like proteins (Ubls) are conjugated to their targets by an enzymatic cascade involving an E1 activating enzyme, an E2 conjugating enzyme, and in some cases an E3 ligase. ISG15 is a Ubl that is conjugated to cellular proteins after IFN-alpha/beta stimulation. Although the E1 enzyme for ISG15 (Ube1L/E1(ISG15)) has been identified, the identities of the downstream components of the ISG15 conjugation cascade have remained elusive. Here we report the purification of an E2 enzyme for ISG15 and demonstrate that it is UbcH8, an E2 that also functions in Ub conjugation. In vitro assays with purified Ub E2 enzymes and in vivo RNA interference assays indicate that UbcH8 is a major E2 enzyme for ISG15 conjugation. These results indicate that the ISG15 conjugation pathway overlaps or converges with the Ub conjugation pathway at the level of a specific E2 enzyme. Furthermore, these results raise the possibility that the ISG15 conjugation pathway might use UbcH8-competent Ub ligases in vivo. As an initial test of this hypothesis, we have shown that a UbcH8-competent Ub ligase conjugates ISG15 to a specific target in vitro. These results challenge the concept that Ub and Ubl conjugation pathways are strictly parallel and nonoverlapping and have important implications for understanding the regulation and function of ISG15 conjugation in the IFN-alpha/beta response.

The human UBE2L6 gene encodes UbcH8(Kumar), a ubiquitin-conjugating enzyme (E2) highly simliar in primary structure to UbcH7 which is encoded by UBE2L3. Like UBC4 and UBC5 in yeast, these proteins demonstrate functional redundancy. Herein we report the intron/exon structure of UBE2L6. Comparison of the genomic organization of UBE2L6 with UBE2L3 demonstrates that these genes remain highly conserved at the genomic as well as at the protein level. We also describe the chromosomal localization of UBE2L6, which maps to chromosome 11q12.