I. No gene transcription occurs in fertilized eggs of the amphibian Xenopus until the mid-blastula transition, (approximately 4000 cells). Therefore all of the appropriate gene products necessary for early development must be stored in the oocyte or egg prior to fertilization. In order to understand the molecular embryology of early amphibian development, we must obtain genes whose products are expressed only in oocytes. We have been working on an oocyte specific gene product called OAX RNA for oocyte activated in Xenopus. This RNA is 181 nucleotides long, present approximately in 10,000 copies/oocyte and is in a cytoplasmic complex of approximately 50S size. This RNA is not found in adult somatic tissue. II. The Aspergillus toxin alpha-sarcin produces a precise cut near the 3'-end of 28S ribosomal RNA in vitro only if the ribosomes are pre-treated with puromycin and EDTA. Alpha-sarcin can also behave as a general nuclease in vitro under appropriate conditions. In order to investigate alpha-sarcin's in vivo activity, we injected it into living Xenopus oocytes and analyzed the resulting RNA. We have also investigated whether ricin and Shiga toxin produce similar effects in oocytes. III. During early development Xenopus replicates its DNA nearly as fast as E. coli in log phase; perhaps indicating that oocytes may be an excellent source of DNA repair activity. We have investigated pyrimidine dimer repair by microinjecting uv- irradiated DNA into oocytes and assaying for repair using 2 methods: (1) Transformation of repair deficient E. coli mutants with the microinjected DNA; (2) Absence of pyrimidine dimers using UV-Endonuclease and denaturing agarose gels.
