Recent technological advancements have allowed for highly-sophisticated mass 
spectrometry-based studies of the histone code, which predicts that combinations 
of post-translational modifications (PTMs) on histone proteins result in defined 
biological outcomes mediated by effector proteins that recognize such marks. 
While significant progress has been made in the identification and 
characterization of histone PTMs, a full appreciation of the complexity of the 
histone code will require a complete understanding of all the modifications that 
putatively contribute to it. Here, using the top-down mass spectrometry approach 
for identifying PTMs on full-length histones, we report that lysine 37 of 
histone H2B is dimethylated in the budding yeast Saccharomyces cerevisiae. By 
generating a modification-specific antibody and yeast strains that harbor 
mutations in the putative site of methylation, we provide evidence that this 
mark exist in vivo. Importantly, we show that this lysine residue is highly 
conserved through evolution, and provide evidence that this methylation event 
also occurs in higher eukaryotes. By identifying a novel site of histone 
methylation, this study adds to our overall understanding of the complex number 
of histone modifications that contribute to chromatin function.