Nuclease C Polymorphism of Calcium-Dependent Nucleases in Chlamydomonas reinhardtii

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Abstract
DNases were extracted from cells of C. reinhardtii. Their polymorphism and metal ion requirements were investigated. Most of the nucleases from this organism required Ca2+ for full activation; therefore, the name nuclease C was given to them. Zn2+ and Mn2+ restored activation, but their respective potencies were 1/8 and 1/32 that of Ca2+. An in situ nuclease assay revealed that there are at least 6 species of nuclease C. The MW 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 [sodium dodecyl sulfate polyacrylamide gel electrophoresis]. Ca2+-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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