| The ubiquitin ligase HectH 9 regulates transcriptional activation by Myc and is essential for tumor cell proliferation . ^^^ Here we show that the E 3 ubiquitin ligase HectH 9 ubiquitinates Myc in vivo and in vitro , forming a lysine 63 linked polyubiquitin chain . ^^^ HectH 9 mediated ubiquitination of Myc is required for transactivation of multiple target genes , recruitment of the coactivator p 300 , and induction of cell proliferation by Myc . ^^^ |