Effects of histone N-terminal tails on DNA processing enzymes and its relevance to genome stability

Abstract

Highly conserved eukaryotic histones are polybasic proteins that package DNA into nucleosomes, a building block of chromatin, allowing extremely long DNA molecules to form compact and discrete chromosomes. The histone N-terminal tails that extend from the nucleosome core act as docking sites for many proteins through diverse posttranslational modifications, regulating various DNA transactions. In this report, we present evidence that the nucleosomes can positively regulate the enzymatic activity of Rad27, a major processing enzyme important for Okazaki fragment in eukaryotes. Individual histones, histone octamers, and nucleosomes are able to stimulate Rad27 in a manner dependent on the N-terminal tails of histones. Kinetic analyses suggest that an increase in catalytic efficiency of Rad27 was mainly due to increased affinity between DNA substrates and Rad27. The physical interaction in vivo between histones and Rad27 results in the enrichment of Rad27 in the vicinity of chromatin, increasing the availability of Rad27 for various DNA metabolisms. These results indicate that nucleosomes are not a mere structural component of chromatin, but an active regulator of DNA metabolisms that serves to ensure the efficient and faithful processing of structural intermediates arising during DNA transactions.