Histone-histone associations within chromatin. Cross-linking studies using tetranitromethane.

Treatment of chromatin with the protein cross-linker tetranitromethane (TNM) results in a product identified as an F2a1-F2b dimer. The same product appears after treatment with TNM of HeLa cells growing in culture. Furthermore acid-extracted histones which have been fractionated into the five separate species can be recombined and mixed with DNA to produce a nucleohistone preparation which is also cross-linked by TNM to give the F2a1-F2b dimer. F1 and F3 can be excluded from the reconstitution mixture without effect on the dimer production. In contrast, the presence of F2a2 is essential to the proper reconstitution of F2a1 and F2b with DNA. The specificity of TNM and the characteristics of the reaction suggest that F2a1 and F2b are cross-linked at their specific binding sites. These results provide evidence that F2a1, F2a2, and F2b interact specifically in chromatin.