Nuclease C Polymorphism of Calcium-Dependent Nucleases in Chlamydomonas reinhardtii

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DNases were extracted from cells of Chlamydomonas reinhardtii. Their polymorphism and metal ion requirements were investigated. Most of the nucleases from this organism required Ca^<2+> for full activation; therefore, the name nuclease C has been given to them. Zn^<2+> and Mn^<2+> restored activation, but their respective potencies were l/8 and l/32 that of Ca^<2+>. An in situ nuclease assay revealed that there are at least 6 species of nuclease C. The molecular weights of the components were 26,000 (C1), 25,000 (C2), 22,000 (C5), 21,000 (C6), 18,000 (C3) and 17,000 (C4) by SDS-PAGE. Ca^<2+>_ dependent nuclease activity was slightly higher in the female gamete than in the male gamete. There was no marked change in the apparent nuclease activity during the first 3 h after mating. An in situ assay, however, showed that nuclease C6 and C4 are present in smaller amounts in the male gamete in comparison to the female gamete, and that the contents or activities of nuclease C5 and C6 diminish during the first 30-60 min after mating. This evidence is discussed in terms of the possible participation of nuclease C in the maternal inheritance of chloroplast genes in this organism.
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