Tandem repeats of the 5' non-transcribed spacer of Tetrahymena rDNA function as high copy number autonomous replicons in the macronucleus but do not prevent rRNA gene dosage regulation.
AUTOR(ES)
Pan, W J
RESUMO
The rRNA genes in the somatic macronucleus of Tetrahymena thermophila are normally on 21 kb linear palindromic molecules (rDNA). We examined the effect on rRNA gene dosage of transforming T.thermophila macronuclei with plasmid constructs containing a pair of tandemly repeated rDNA replication origin regions unlinked to the rRNA gene. A significant proportion of the plasmid sequences were maintained as high copy circular molecules, eventually consisting solely of tandem arrays of origin regions. As reported previously for cells transformed by a construct in which the same tandem rDNA origins were linked to the rRNA gene [Yu, G.-L. and Blackburn, E. H. (1990) Mol. Cell. Biol., 10, 2070-2080], origin sequences recombined to form linear molecules bearing several tandem repeats of the origin region, as well as rRNA genes. The total number of rDNA origin sequences eventually exceeded rRNA gene copies by approximately 20- to 40-fold and the number of circular replicons carrying only rDNA origin sequences exceeded rRNA gene copies by 2- to 3-fold. However, the rRNA gene dosage was unchanged. Hence, simply monitoring the total number of rDNA origin regions is not sufficient to regulate rRNA gene copy number.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=306898Documentos Relacionados
- Locating transcribed and non-transcribed rDNA spacer sequences within the nucleolus by in situ hybridization and immunoelectron microscopy.
- Site-specific initiation of DNA replication within the non-transcribed spacer of Physarum rDNA.
- Regular distribution of length heterogeneities within non-transcribed spacer regions of cloned and genomic rDNA of Saccharomyces cerevisiae.
- The nucleotide sequence of an unusual non-transcribed spacer and its ancestor in the rDNA in Chironomus thummi.
- New tandem repeat region in the non-transcribed spacer of human ribosomal RNA gene.