Eukaryotic DNA is organized with histone proteins in specific complexes called chromatin. Condensed chromatin, heterochromatin, prevents transcription of genes. Partial DNAse digestion of chromatin reveals its nucleosome structure. The histone variant H2AX constitutes about 10% of the H2A histones in human chromatin. The nucleosome is the fundamental subunit of chromatin. Chromosomes in eukaryotes are composed of chromatin fiber. Ramakrishnan is also known for his past work on histone and chromatin structure. This link between DNA methylation and chromatin structure is very important. Polycomb-group proteins play a role in regulating genes through modulation of chromatin structure. The process is guided by small RNAs and epigenetic chromatin marks. These proteins organize the DNA into a compact structure called chromatin. Histone modifications modulate the packing of chromatin. The human genome was annotated with chromatin states. Hepatocyte nuclei are round with dispersed chromatin and prominent nucleoli. Thirdly, ICAT labeling was recently combined with chromatin isolation to identify and quantify chromatin-associated proteins.