Homology model building of Hho1p supports its role as a yeast histone H1 protein

Biochemical studies to date have not been able to identify the linker histone H1 protein in the budding yeast Saccharomyces cerevisiae. Database homology searching against the complete yeast genome has identified a gene, HHO1, (or YPL127C, formerly LPI17) which encodes a protein that has two regions that show similarity to the pea histone H1 globular domain. To determine whether Hho1p can assume the shape of an H1 protein, homology model building experiments were performed using the structure of chicken histone H5 globular domain as the basis for comparison. A statistically significant match between each of the two globular domains of Hho1p and the chicken histone H5 structure was obtained, and probability values indicate that there is a less than 1 in 100 chance that such a match would be the result of a random event. These findings support the proposal that Hho1p acts as an "H1 dimer" and could be responsible for the decreased linker DNA length observed between nucleosomal core particles.