Abstract
Two specific slow sedimenting nucleoprotein particles containing equimolar amounts of histones H2A and H2B and 38 or 49 base pair (bp) lengths of DNA have been isolated by centrifugation on sucrose gradients. The 3.4S particles containing 38 bp DNA and H2A+H2B thermally denature at 61 degrees, considerably higher than Proteinase K treated particles (44 degrees), but lower than 11S nucleosomes (76 degrees). Treatment with Proteinase K increases the circular dichroism of 3.4S particles at 280 nm by 63% and decreases the sedimentation coefficient to 2.1S. These results indicate that H2A and H2B are proximate along DNA in nucleosomes and alone can alter the optical activity and perhaps conformation of local regions of DNA.