Uniparental inheritance of the chloroplast genome has been observed in a wide variety of green plants.In Chlamydomonas this phenomenon, which can be selectively inhibited by UV irradiation of mt+ gametes, has been shown cytologically to be due to the preferential degradation of mt--derived chloroplast nucleoids in young zygotes. The zygote-specific pair of zy1 genes, zys1A and zys1B,is expressed earliest among live genes isolated from a '10-min' zygote library. We report here that the ZYS1 protein, which is encoded by the invertedly duplicated zys1 gene, accumulates in zygotes and is localized in nuclei. In addition, when mt+ gametes (but not mt- gametes) are UV-irradiated before mating, only very limited accumulation of ZYS1 protein can be detected in the resulting zygotes.
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