Open AccessA Promoter Region Mutation Affecting Replication of the Tetrahymena Ribosomal DNA Minichromosome
Author(s) -
Renata C. Gallagher,
Elizabeth H. Blackburn
Publication year - 1998
Publication title -
molecular and cellular biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.14
H-Index - 327
eISSN - 1067-8824
pISSN - 0270-7306
DOI - 10.1128/mcb.18.5.3021
Subject(s) - biology , minichromosome maintenance , minichromosome , tetrahymena , origin recognition complex , ribosomal dna , origin of replication , genetics , control of chromosome duplication , eukaryotic dna replication , pre replication complex , dna replication , microbiology and biotechnology , transcription (linguistics) , dna replication factor cdt1 , gene , chromosome , phylogenetics , linguistics , philosophy
In the ciliated protozoanTetrahymena thermophila the ribosomal DNA (rDNA) minichromosome replicates partially under cell cycle control and is also subject to a copy number control mechanism. The relationship between rDNA replication and rRNA gene transcription was investigated by the analysis of replication, transcription, and DNA-protein interactions in a mutant rDNA, thermm3 rDNA. Thermm3 (for rDNA maturation or maintenance mutant 3) rDNA contains a single-base deletion in the rRNA promoter region, in a phylogenetically conserved sequence element that is repeated in the replication origin region of the rDNA minichromosome. The multicopyrmm3 rDNA minichromosome has a maintenance defect in the presence of a competing rDNA allele in heterozygous cells. No difference in the level of rRNA transcription was found between wild-type andrmm3 strains. However,rmm3 rDNA replicating intermediates exhibited an enhanced pause in the region of the replication origin, roughly 750 bp upstream from thermm3 mutation. In footprinting of isolated nuclei, thermm3 rDNA lacked the wild-type dimethyl sulfate (DMS) footprint in the promoter region adjacent to the base change. In addition, a DMS footprint in the origin region was lost in thermm3 rDNA minichromosome. This is the first reported correlation in this system between an rDNA minichromosome maintenance defect and an altered footprint in the origin region. Our results suggest that a promoter region mutation can affect replication without detectably affecting transcription. We propose a model in which interactions between promoter and origin region complexes facilitate replication and maintenance of theTetrahymena rDNA minichromosome.