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Cdc34 is an E2 ubiquitin- conjugating enzyme that functions in conjunction with SCF (Skp1·Cullin 1·F-box) E3 ubiquitin ligase to catalyze covalent attachment of polyubiquitin chains to a target protein. Here we identified direct interactions between the human Cdc34 C terminus and ubiquitin using NMR chemical shift perturbation assays. The ubiquitin binding activity was mapped to two separate Cdc34 C-terminal motifs (UBS1 and UBS2) that comprise residues 206-215 and 216-225, respectively. UBS1 and UBS2 bind to ubiquitin in the proximity of ubiquitin Lys48 and C-terminal tail, both of which are key sites for conjugation. When bound to ubiquitin in one orientation, the Cdc34 UBS1 aromatic residues (Phe206, Tyr207, Tyr210, and Tyr211) are probably positioned in the vicinity of ubiquitin C-terminal residue Val70. Replacement of UBS1 aromatic residues by glycine or of ubiquitin Val70 by alanine decreased UBS1-ubiquitin affinity interactions. UBS1 appeared to support the function of Cdc34 in vivo because human Cdc34(1-215) but not Cdc34(1-200) was able to complement the growth defect by yeast Cdc34 mutant strain. Finally, reconstituted IκBα ubiquitination analysis revealed a role for each adjacent pair of UBS1 aromatic residues (Phe206/Tyr207, Tyr210/ Tyr211) in conjugation, with Tyr210 exhibiting the most pronounced catalytic function. Intriguingly, Cdc34 Tyr210 was required for the transfer of the donor ubiquitin to a receptor lysine on either IκBα or a ubiquitin in a manner that depended on the neddylated RING subcomplex of the SCF. Taken together, our results identified a new ubiquitin binding activity within the human Cdc34 C terminus that contributes to SCF-dependent ubiquintination. [ABSTRACT FROM AUTHOR]

Histone-modifying enzymes play a pivotal role in gene expression and repression. In human, DOT1L (Dot1-like) is the only known histone H3 lysine 79 methyltransferase. hDOT1L is associated with transcriptional activation, but the general mechanism connecting hDOT1L to active transcription remains largely unknown. Here, we report that hDOT1L interacts with the phosphorylated C-terminal domain of actively transcribing RNA polymerase II (RNAPII) through a region conserved uniquely in multicellular DOT1 proteins. Genomewide profiling analyses indicate that the occupancy of hDOT1L largely overlaps with that of RNAPII at actively transcribed genes, especially surrounding transcriptional start sites, in embryonic carcinoma NCCIT cells. We also find that C-terminal domain binding or H3K79 methylations by hDOT1L is important for the expression of target genes such as NANOG and OCT4 and a marker for pluripotency in NCCIT cells. Our results indicate that a functional interaction between hDOT1L and RNAPII targets hDOT1L and subsequent H3K79 methylations to actively transcribed genes. [ABSTRACT FROM AUTHOR]