Abstract
The number of ribosomal RNA genes and the rate of ribosomal RNA synthesis have been analyzed in a mutant of Xenopus laevis carrying two partial nucleolar organizers (p 1−1/p1−2 nu). The p 1−1 and p 1−2 nucleolar organizers have fewer ribosomal RNA genes than the normal (+ nu) organizer, and each produces a smaller nucleolus than the + nu organizer in heterozygous embryos (+/p 1−1 and +/p 1−2). These heterozygotes develop normally and synthesize ribosomal RNA at normal rates. The p 1−1/p1−2 nu mutants die at an early stage of development, and they synthesize ribosomal RNA at only 50% of the normal rate even though they have 70% of the haploid number of ribosomal RNA genes. These results show that the ribosomal RNA genes contained in a partial nucleolar organizer are not transcribed with the same efficiency as those found in an intact organizer and suggest the existence of genes, within the nucleolar organizer, which control the transcription of ribosomal RNA.
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This investigation was supported by a U.S. Public Health Service Research Grant No. CA-39, 026-01A1 to L. M. from the National Cancer Institute and by a scholarship for training in research methods to J. K. from the Medical Research Council of Great Britain.
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Miller, L., Knowland, J. The number and activity of ribosomal RNA genes in Xenopus laevis embryos carrying partial deletions in both nucleolar organizers. Biochem Genet 6, 65–73 (1972). https://doi.org/10.1007/BF00485967
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DOI: https://doi.org/10.1007/BF00485967