The Elp3 subunit of human Elongator complex is functionally similar to its counterpart in yeast

Functions of the Elp3 subunit of the recently purified human Elongator were studied using an in vivo yeast complementation system. We demonstrated that the human ELP3 gene (hELP3) was able partially to complement functional defects of yeast elp3Delta cells. Furthermore, a chimeric ELP3 gene (yhELP3) encoding a protein in which the putative histone acetyltransferase (HAT) domain of hELP3 fused to the remainder of the yeast Elp3p corrected the growth defects of elp3Delta cells and complemented the slow activation of some inducible genes. Moreover, deletion of the B motif of the catalytic domain of the HAT region of hELP3 eliminated the ability of yhELP3 to complement elp3Delta in vivo, indicating that the HAT activity is essential for ELP3 function. We also demonstrated that replacement of specific lysine residues in histones H3 and H4 by arginine affected the complementation capacity of both the yeast gene (yELP3) and the chimeric yhELP3 in the elp3Deltastrain. Specifically, mutation of lysine-14 of H3 (H3 K14R) or lysine-8 of H4 (H4 K8R) reduced the ability of yELP3 and yhELP3 to complement the elp3Delta mutant, whereas simultaneous mutation of both sites (H3 K14R/H4 K8R) almost completely abolished complementation. These results imply a link between the acetylation of specific sites in nucleosomal histones and the regulation of transcription elongation by human Elp3. The data presented in this report suggest that the Elp3 subunits of human and yeast are highly conserved in their structure and functions.