Browsing by Author "Landsman, David"

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    Deoxyribonuclease probing on sea urchin embryo chromatin
    (1983) Landsman, David
    The role that the sea urchin, Parechinus angulosus, embryo and sperm histone variants play in chromatin structure has been investigated. Chromatin structure has been determined at different levels of resolution in sperm and in developing embryos using micrococcal nuclease, pancreatic deoxyribonuclease (DNase I) and restriction endonucleases. Micrococcal nuclease and restriction endonuclease digestions of sea urchin gastrula chromatin have been analysed and it is shown that it is not possible to isolate large polynucleosomal chromatin complexes which are soluble in low ionic strength buffers. The nucleosomal DNA repeat lengths for sea urchin blastula, gastrula and sperm have been determined using micrococcal nuclease. The repeat length for sperm is significantly larger than blastula and gastrula repeat lengths whereas blastula and gastrula repeat lengths are not significantly different. Nucleosomal core particles have been isolated from early blastula, gastrula and sperm of sea urchins. After DNase I digestion of 51-labelled core particles the rate constants of cutting of the DNA at the susceptible sites on these core particles have been determined. The DNase I digestion kinetics of blastula and gastrula core particles are similar whereas sperm core particles are digested at a slower rate, mainly at the sites which are closest to the ends of the core particle DNA. Also, a site, which is 5 bases on the outside of the core particle and which is partially protected from nuclease attack, has been identified. The implications of these findings in relation to the histone variants in embryos and sperm of sea urchins are discussed.