5-methylcytosine is localized in nucleosomes that contain histone H1

We have developed a procedure for purifying highly specific polyclonal antibodies against 5-methylcytosine. These antibodies were used to probe the distribution of 5-methylcytosine among fractionated nucleosomes of mouse cell chromatin. Our results demonstrate that at least 80% of the 5-methylcytosine is localized in nucleosomes that contain histone H1. Native nucleosomes that lack histone H1 or possess high mobility group proteins package DNA that is 1.6- to 2.3-fold undermethylated. We suggest that the preferential association of methylated sequences with histone H1 has functional significance because DNA methylation has been linked to gene inactivation and histone H1 is known to promote chromatin condensation.