Background: Changes in chromatin structure play a large role in the regulation of transcription in eukaryotes (1). The nucleosome is the primary building block of chromatin, and is made up of four core histone proteins (H2A, H2B, H3 and H4) (2). Acetylation of core histones regulates gene expression (2). Histone H2B is primarily acetylated at lysines 5, 12, 15, and 20 (3). Ubiquitylation of Histone H2B at lysine 123 by Rad6 has been implicated in transcriptional activation and lysine methylation on histone H3 (4).