The chief objective of the proposed research is to learn more about genome organization and RNA transcription in a higher eukaryote. Particular attention will be devoted to the synthesis of RNA on the loops of the giant lampbrush chromosome of the newt, Notophthalmus. A variety of radioactive DNA probes will be hybridized in situ to the RNA of the chromosome in order to determine what sequences are being transcribed in the oocyte. The probes will be constructed by recombinant DNA methods and will include, in addition to random clones, the genes coding for 5S RNA, histone mRNA, globin mRNA and various oocyte-specific RNAs. The fine structure of the various probes will be analyzed by restriction endonuclease digestion, nucleic acid hybridization (Southern blots) and in some cases by direct DNA sequencing. Interferences about the transcription of the probes during oogenesis will be derived from the cytological features of the in situ hybrids.