The basis set of protein forms expressed by human cells from the H2B gene family 
was determined by Top Down Mass Spectrometry. Using Electron Capture 
Dissociation for MS/MS of H2B isoforms, direct evidence for the expression of 
unmodified H2B.Q, H2B.A, H2B.K/T, H2B.J, H2B.E, H2B.B, H2B.F, and monoacetylated 
H2B.A was obtained from asynchronous HeLa cells. H2B.A was the most abundant 
form, with the overall expression profile not changing significantly in cells 
arrested in mitosis by colchicine or during mid-S, mid-G2, G2/M, and mid-G1 
phases of the cell cycle. Modest hyperacetylation of H2B family members was 
observed after sodium butyrate treatment.