The genomes of higher organisms are packaged in nucleosomes with functional 
histone modifications. Until now, genome-wide nucleosome and histone 
modification studies have focused on transcription start sites (TSSs) where 
nucleosomes in RNA polymerase II (RNAPII) occupied genes are well positioned and 
have histone modifications that are characteristic of expression status. Using 
public data, we here show that there is a higher nucleosome-positioning signal 
in internal human exons and that this positioning is independent of expression. 
We observed a similarly strong nucleosome-positioning signal in internal exons 
of Caenorhabditis elegans. Among the 38 histone modifications analyzed in man, 
H3K36me3, H3K79me1, H2BK5me1, H3K27me1, H3K27me2, and H3K27me3 had evidently 
higher signals in internal exons than in the following introns and were clearly 
related to exon expression. These observations are suggestive of roles in 
splicing. Thus, exons are not only characterized by their coding capacity, but 
also by their nucleosome organization, which seems evolutionarily conserved 
since it is present in both primates and nematodes.