Preferential transcription of Xenopus laevis ribosomal RNA in interspecies hybrids between Xenopus laevis and Xenopus mulleri

摘要: Abstract Ribosomal RNA synthesized by hybrid frogs from the cross between Xenopus laevis and mulleri was analyzed molecular hybridization with purified ribosomal DNA each species. Although 18 S 28 rRNA sequences are indistinguishable these two species, remaining 10% of 40 precursor molecule species hybridizes about tenfold more efficiently to homologous rDNA than heterologous rDNA. Using an assay based upon this fact, we show that in X. is transcribed preferentially repressed. repressed regardless which female parent. The repression nearly complete throughout early embryogenesis until swimming tadpole stage, after a low level synthesis detectable total embryo population. Some adult made no rRNA, whereas others were found substantial amounts. Transcription embryos female, heterozygous for deletion mutation, wild type male. Half contain only eventually but onset much later embryos. In reverse (female × male heterozygote) turn-on not delayed. results four types crosses indicate either or maternal cytoplasm can repress expression presence be permanent. transient usually reversible.