Interaction of non-histone proteins HMG1 and HMG2 with core histones in nucleosomes and core particles revealed by chemical cross-linking.

Chemical cross-linking was used to study the interaction of the non-histone chromosomal proteins HMG1 and HMG2 with core histones in H1,H5-depleted nucleosomes or core particles. Cross-linking with a 'zero-length' cross-linker 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and with a longer (cleavable) cross-linker dimethyl-3,3'-dithiobispropionimidate revealed an interaction of HMG1 and HMG2 with (or proximity to) core histones in both types of particles. These results indicated that the presence of the 40-50-base-pairs-long segment of the 'linker' DNA in nucleosomes was not necessary for the establishment of mutual contacts of HMG1 and HMG2 proteins with core histones. Possible implications of the interaction of HMG1 and HMG2 proteins with histones for the structure and functioning of chromatin are discussed.