Effects of aurintricarboxylic acid and formaurindicarboxylic acid on nuclei and chromatin

Abstract

Aurintricarboxylic acid and formaurindicarboxylic acid were used as a low molecular weight probe for the analysis of chromatin structure. These dyes induced strong nuclear swelling. The swelling reaction was monitored by the turbidity change of nuclear suspension. A stoichiometric relationship was suggested between the concentration of aluminon (ammonium aurintricarboxylic acid) at which maximal nuclear swelling occurred and the amount of nuclear DNA in the system. The swelling velocity was much slower at pH 5.4 than at pH 7.9. The swelling time course at pH 5.4 consisted of four distinct successive steps with different swelling velocities. In the presence of 1 m m Ca 2+ aluminon failed to induce nuclear swelling. The inhibition was slight, however, if Ca 2+ was added after initiation of swelling. Centrifugation of chromatin treated with formaurindicarboxylic acid in a linear gradient of sucrose revealed decreased chromatin density and dissociation of histones from the chromatin. After the dissociation H3 and H4 histones formed aggregates of various size. From the binding of formaurindicarboxylic acid to nuclei, the apparent binding parameters were estimated for intranuclear binding sites.