Yeast histone H2B containing large amino terminus deletions can function in vivo

The basic amino terminus of each histone is external to the nucleosome core particle. In vitro studies have shown that the amino termini are not required for nucleosome assembly. To address the significance of these results in vivo we constructed mutations in yeast histone H2B in genetic backgrounds lacking wild-type H2B protein. We found that the protein can function in vivo even with large deletions at its amino terminus. These mutations produce no obvious phenotype and there appears to be no selection against the mutant proteins in chromatin assembly. A deletion removing a large portion of the carboxyl terminus was lethal. We conclude that much of the amino terminus of histone H2B has no essential function in vivo.