Specific distribution of the Saccharomyces cerevisiae linker histone homolog HHO1p in the chromatin

In virtually all eukaryotic organisms, linker DNA between nucleosomes is as sociated with a histone termed linker histone or histone H1. In Saccharomyc es cerevisiae, HHO1 encodes a putative linker histone with very significant homology to histone H1. The encoded protein is expressed in the nucleus, b ut has not been shown to affect global chromatin structure, nor has its del etion shown any detectable phenotype. In vitro chromatin assembly experimen ts with recombinant HHO1p have shown that it is able to complex with dinunc leosomes in a similar manner to histone H1. Here we report that while disru ption of HHO1 has little affect on RNA levels of most cellular transcripts, there are numerous exceptions. Measurement of HHO1 p concentration in the wild-type cell showed a stoichiometry of about one HHO1 p molecule per 37 n ucleosomes. Localization of HHO1 p in the chromatin, using an immunoprecipi tation technique, showed preferential HHO1p binding to rDNA sequences. Thes e results suggest that HHO1p may play a similar role to linker histones, bu t at restricted locations in the chromatin.