Histone H5 can increase the internucleosome spacing in dinucleosomes to nativelike values.

Chicken erythrocyte chromatin was assembled with inner histones at about 60% of the ratio found in vivo and subsequently incubated with histone H5 (or H1 + H5) in a solution containing 0.1 M NaCl and poly(glutamic acid). Micrococcal nuclease digestion produced dinucleosomes of 360-390 base pair (bp) DNA content, similar to those from native chromatin and contrasting with the 270-280 bp species found in material incubated without H5. On sucrose gradients a dinucleosome sedimenting at 16 S containing 360 bp DNA was isolated. Removal of H1 + H5 after reconstitution did not change these results; H5 thus can induce rearrangements of nucleosome cores with respect to their neighbors. The results are interpreted as an H5-induced "sliding apart" of histone octamers, complementary to the "sliding together" found in native chromatin after removal of H1 + H5.

The characterisation of a 5-S 'monosome' fraction from chromatin of Physarum polycephalum.

A so-called '5-S mononucleosome' fraction was isolated from nuclei of Physarum polycephalum by digestion with micrococcal nuclease and subsequent fractionation by gel filtration. This fraction had electrophoretic and sedimentation properties which were similar to DNA of approximately 140 base pairs in length. It is shown that lysis of the nuclei activates a protease which is resistant to phenyl-methyl sulphonyl fluoride, o-phenanthroline and parachloromercuri benzene sulphonate and which subsequently degrades the nucleosomes.

Analysis of the high mobility group proteins associated with salt-soluble nucleosomes.

Two methods have recently been described for the isolation of monomer nucleosomes enriched in transcribed sequences which depend on their solubility in 0.1 M NaCl (Levy, W.B. and Dixon (1978), Nucleic Acid Res., 5, 4155-4163) or solutions containing divalent metal ions (Bloom, K.S. and Anderson, J.N. (1978), Cell, 15, 141-150). Using these procedures the proteins associated with such nucleosomes from rabbit thymus, calf liver and hen oviduct nuclei were isolated and analysed. Increased amounts of proteins HMG14 AND HMG17 and small amounts of HMG1 and HMG2 were found associated with the four core histones H2A, H2B, H3 and H4 in these nucleosomes. HMG14 and HMG17 were found to be enriched 2 - 7 fold, suggesting an involvement of these two proteins with transcribed sequences. 0.1 M NaCl-soluble monomer nucleosomes prepared by the method of Levy and Dixon were analysed by polyacrylamide gel electrophoresis and found to be composed of principally two types of particle: 1. Core particles of 145 base pairs of DNA associated with the four core histones only. 2. Nucleosomes with 160 base pairs of DNA associated with the four core histones, increased amounts of HMG14 and 17, and no H1. Small amounts of HMG1 and HMG2 are also detected. These results suggest that HMG14 and HMG17 might be interacting with the 15 base pair linker DNA. A model is presented for the structure of transcriptionally active chromatin.