Affinity of HMG17 for a mononucleosome is not influenced by the presence of ubiquitin-H2A semihistone but strongly depends on DNA fragment size

Abstract

We have used a two-dimensional (deoxyribonucleoprotein →DNA) electrophoretic binding assay to study the interaction of the purified high mobility group protein HMG17 with isolated HeLa mononucleosomes as a function of their DNA fragment size and the presence of ubiquitin-H2A semihistone. No significant differences between affinities of HMG17 for ubiquitinated and non-ubiquitinated core mononucleosomes were observed. In striking contrast, the apparent affinity of HMG17 for a mononucleosome increases more than 100-fold upon an increase of the length of the mononucleosomal DNA fragment by as few as 3 to 5 bp over the core DNA length ({reversed tilde}146 bp). We suggest that the magnitude of this effect is sufficient to explain the preferential binding of HMG17 in vitro to mononucleosomes derived from actively transcribed genes. © 1983 IRL Press Limited.