Qualitative and Quantitative Studies on DNA and RNA Synthesis in Loxodes striatus Nuclei*

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Abstract
The characteristics of DNA and RNA synthesis in the nuclei of Loxodes were investigated. L. striatus is a primitive ciliate with 2 pairs of structurally differentiated diploid nuclei, the macro- and micronuclei. The macronuclei are differentiated morphologically into a clearly recognizable central core and an outer zone. To determine DNA and RNA synthesis, individual organisms were analyzed by autoradiography after incubating groups of cells with a 3H-labeled precursor ([3H]thymidine for DNA and [3H]uridine for RNA). All portions of macro- and micronuclei appeared to contain DNA as judged by the localizations of incorporated [3H]thymidine. The macro- and micronuclei did not synthesize DNA at the same time; moreover, the duration of DNA synthesis in the former was much longer than of the latter nucleus. Replication of DNA in the inner core and outer zone of the macronucleus occurred at separate times with little if any overlap. All of the detectable [3H]uridine incorporation was found in the macronucleus and none in the micronucleus. Within the macronucleus the central core was more heavily labeled. The quantitative differences in the label of the different components of the nuclear complex were investigated. Contrary to previous information DNA synthesis can occur in adult macronuclei. The possible explanation of these results is discussed in the context of the nuclear evolution of ciliates and of recent information on nuclear differentiation.