PURPOSE Repetitive ribosomal DNA (rDNA) genes are GC-rich clusters in the human genome. The aim of the study was to determine the methylation status of two rDNA subunits, the 18S and 28S genes, in ovarian tumors and to correlate methylation levels with clinicopathologic features in a cohort of ovarian cancer patients. EXPERIMENTAL DESIGN 18S and 28S rDNA methylation was examined by quantitati...

Tetrahymena thermophila has been transformed to paromomycin-resistant phenotypes by microinjection of an aminoglycoside 3'-phosphotransferase (neo) gene under the control of the T. thermophila histone H4-I promoter. This chimeric neo gene, by itself or on a vector containing a rRNA-encoding DNA (rDNA) origin of replication, transforms T. thermophila. In cells transformed with the rDNA origin ve...

The yeast SIR2 gene maintains inactive chromatin domains required for transcriptional repression at the silent mating-type loci and telomeres. We previously demonstrated that SIR2 also acts to repress mitotic and meiotic recombination between the tandem ribosomal RNA gene array (rDNA). Here we address whether rDNA chromatin structure is altered by loss of SIR2 function by in vitro and in vivo a...

The ribosomal RNA (rRNA) gene encodes rRNA for protein synthesis. Aberrant expression of the rRNA gene has been generally observed in tumor cells and levels of its promoter methylation as an epigenetic regulator affect rRNA gene transcription. The possible relationship between expression and promoter methylation of rDNA has not been examined in human clinical cervical cancer. Here we investigat...

Concerted evolution is the production and maintenance of homogeneity within repeated families of DNA. Two mechanisms--unequal crossing over and biased gene conversion--have been the principal explanations of concerted evolution. Concerted evolution of ribosomal DNA (rDNA) arrays is thought to be largely the result of unequal crossing over. However, concerted evolution of rDNA in parthenogenetic...

Ribosome biogenesis dictates the translational capacity of cells. Several mechanisms establish and maintain transcriptional output from eukaryotic ribosomal DNA (rDNA) loci. rDNA silencing is one such mechanism that ensures the inactivity and hence the maintenance of a silenced state of a subset of rRNA gene copies. Whereas oncogenic agents stimulate rRNA gene transcription, tumor suppressors d...

Dynamic changes in gene positioning contribute to differential expression of virulence-related gene families in protozoan pathogens; however, the role of nuclear architecture in gene expression in the human malaria parasite Plasmodium falciparum remains poorly understood. Here we investigated the developmentally regulated ribosomal RNA (rRNA) gene family in P. falciparum, which, unlike that in ...

Epigenetic changes accompanying plant cell dedifferentiation and differentiation are reported in 35S ribosomal DNA (rDNA) of tobacco (Nicotiana tabacum). There was a reduction of CG and CNG methylation in both intergenic and genic regions of the rDNA cistron in fully dedifferentiated callus and root compared to leaf. The rDNA hypomethylation was not random, but targeted to particular rDNA gene ...

RNA polymerase II (Pol II)-transcribed genes embedded within the yeast rDNA locus are repressed through a Sir2-dependent process called 'rDNA silencing'. Sir2 is recruited to the rDNA promoter through interactions with RNA polymerase I (Pol I), and to a pair of DNA replication fork block sites (Ter1 and Ter2) through interaction with Fob1. We utilized a reporter gene (mURA3) integrated adjacent...

The Sir2 protein mediates gene silencing and repression of recombination at the rDNA repeats in budding yeast. Here we show that Sir2 executes these functions as a component of a nucleolar complex designated RENT (regulator of nucleolar silencing and telophase exit). Net1, a core subunit of this complex, preferentially cross-links to the rDNA repeats, but not to silent DNA regions near telomere...