The number and activity of ribosomal RNA genes inXenopus laevisembryos carrying partial deletions in both nucleolar organizers
✍ Scribed by Leo Miller; John Knowland
- Publisher
- Springer
- Year
- 1972
- Tongue
- English
- Weight
- 494 KB
- Volume
- 6
- Category
- Article
- ISSN
- 0006-2928
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✦ Synopsis
The number of ribosomal RNA genes and the rate of ribosomal RNA synthesis have been analyzed in a mutant ofXenopus laevis carrying two partial nucleolar organizers (pl-a/pl-2 nu). The p 1-1 and pl-2 nueleolar organizers have fewer ribosomal RNA genes than the normal (+ nu) organizer, and each produces a smaller nueleolus than the + nu organizer in heterozygous embryos (+/p1-i and +/pl-2). These heterozygotes develop normally andsynthesize ribosomal RNA at normal rates. The pi-1/pl-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.