The purpose of this study was to examine the regeneration of periodontal tissue after the application of recombinant human bone morphogenetic protein-2 (rhBMP-2) to horizontal circumferential defects created by experimental periodontitis. Twelve mandibular second premolars in 6 adult beagle dogs were subjected to experimental periodontal breakdown by placing silk ligatures around the teeth until the bone loss exceeded half of the root length. Flap surgery was then performed and the exposed cementum removed. The distance between the bone crest and cemento-enamel junction (CEJ) was about 5 mm. RhBMP-2 (40 micrograms/100 microliters) with a sponge-type carrier material made of gelatin and polylactic acid polyglycolic acid copolymer was placed in the furcation area (5 mm x 5 mm x 5 mm) and around the roots (10 mm x 5 mm x 2.5 mm x 2 pieces). In the control group, the same carrier material without rhBMP-2 was placed in the same manner. The flaps were replaced and sutured to cover these materials completely. Twelve weeks after surgery, the animals were sacrificed and serial sections were prepared in a bucco-lingual plane. Considerable new bone formation was observed in the rhBMP-2-treated sites. New cementum with Sharpey's fibers was observed on the instrumented root surface. On histometric analysis, the amount of new bone, new cementum, and connective tissue attachment was significantly greater in the rhBMP-2-treated group (paired t test; P < 0.01). These results indicate that suitable application of rhBMP-2 can produce considerable periodontal tissue regeneration, even in cases of horizontal circumferential defects.

A protein, which facilitates assembly of a nucleosome-like structure in vitro, was previously partially purified from mouse FM3A cells [Ishimi, Y. et al. (1 983) J . Biochem. (Tokyo) 94,735 -7441. The protein has been purified to approximately 80 from FM3A cells by using histone-Sepharose column chromatography. It sedimented at 4.6 S and had a molecular mass of 53kDa. A preincubation of core histones with the 53-kDa peptide before DNA addition was necessary for the nucleosome assembly. The 53-kDa peptide bound to core histones and formed a 12-S complex. This complex contained stoichiometrical amounts of the 53-kDa peptide and core histones, and the core histones in this complex were composed of equal amounts of H2A, H2B, H3 and H4 histones. The nucleosomes were assembled by adding pBR322 DNA to the 12-S complex. When mononucleosome DNA and core histones were mixed in the presence of the 53-kDa peptide, formation of a 10.5-S complex was observed. The complex contained DNA and core histones in equal amounts, while no 53-kDa peptide was detected in the complex.From above results it is suggested that the 53-kDa peptide facilitates nucleosome assembly by mediating formation of histone octarner and transferring it to DNA. Rat antibody against the 53-kDa peptide did not bind to nucleoplasmin from Xenopus eggs. The relationship between the 53-kDa peptide and nucleoplasmin is discussed.In eukaryotic cells, chromatin consists of a repeating unit called a 'nucleosome', which contains about 200 base-pairs of DNA, two molecules each of H2A, H2B, H3 and H4 histones, and one molecule of HI histone [1,2]. In many mammalian cells almost all core histones (H2A, H2B, H3, H4) are synthesized at S phase and their synthesis is coupled with DNA synthesis [3 -51. However, basal histone synthesis is observed also at GI phase in some cells [6], and mouse lymphoma cell synthesizes core histones at G I phase at the same level as S phase [7,8].As to the mode of deposition of newly synthesized histone on DNA, several confusing results have been presented. From the observation of the group of Weintraub [9-111, it is suggested that new histones are bound to the lagging strand of replicated DNA and they are assembled conservatively into an octamer. On the other hand, Jackson et al. [12,13] indicated that new H3 and H4 histones were bound to replicating DNA, while new H2A and H2B histones were deposited on nonreplicating DNA rather than the replicating DNA. There are several reports indicating that new histones are distributed equally to both daughter strands [14,15]. In any case it is not well examined whether new histones are bound to DNA by a single step as an octamer or by multiple steps.There are several factors which facilitatc nucleosome assembly in t'itro at physiological ionic strength. Nucleoplasmin (29 kDa), which has been discovered in Xenopus eggs by Laskey et al. [I 6,171, facilitate nucleosome assembly by the interaction with core histones. Experiments using its fluorescent antibody suggested that it exists in mammalian cells [...

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