The transcription of ribosomal RNA genes (rDNA) is a rate-limiting step in ribosome biogenesis and changes profoundly in response to environmental conditions. Recently we reported that JmjC demethylase KDM2A reduces rDNA transcription on starvation, with accompanying demethylation of dimethylated Lys 36 of histone H3 (H3K36me2) in rDNA promoter. Here, we characterized the functions of two domai...

Transcriptional silencing in Saccharomyces cerevisiae occurs at the silent mating-type loci HML and HMR, at telomeres, and at the ribosomal DNA (rDNA) locus RDN1. Silencing in the rDNA occurs by a novel mechanism that depends on a single Silent Information Regulator (SIR) gene, SIR2. SIR4, essential for other silenced loci, paradoxically inhibits rDNA silencing. In this study, we elucidate a re...

Eco-RI-A fragments of the human ribosomal RNA gene family from two types of tissue and three individuals were cloned in lambda vectors and compared by restriction enzyme digestion and electron microscopy. The EcoRI fragment A contains (i) 0.2 kb of the 3' end of the 18S rDNA, (ii) 2.5 kb of internal transcribed spacer and the 5.8S rDNA, and (iii) 4.6 kb of the 28S rDNA gene. All of the six clon...

Genomic instability is a conserved factor in lifespan reduction, although the molecular mechanism is not known. Studies in the yeast Saccharomyces cerevisiae over the past 20 years have found a connection between the ribosomal RNA gene cluster (rDNA) and lifespan. The highly repetitive rDNA exhibits genomic instability, and the antiaging histone deacetylase gene SIR2 regulates this instability....

rDNA loci, composed of hundreds of tandemly duplicated arrays of rRNA genes, are known to be among the most unstable genetic elements due to their repetitive nature. rDNA instability underlies aging (replicative senescence) in yeast cells, however, its contribution to the aging of multicellular organisms is poorly understood. In this study, we investigate the dynamics of rDNA loci during aging ...

The ribosomal DNA (rDNA) in Tetrahymena thermophila is a 21-kilobase-pair palindromic DNA molecule that replicates autonomously in the macronucleus and is maintained at the level of about 10,000 copies per macronucleus. The rDNA of inbred strain C3 outreplicates the rDNA of inbred strain B in most B/C3 heterozygous macronuclei, generating macronuclei containing exclusively C3 rDNA sequences. In...

Aim. 5S ribosomal DNA (5S rDNA) represents a universal model for studying the evolution of repeated sequences in eukaryotic organisms. Taking into account that this region genome still remains almost undescribed species family Sapindaceae, we investigated molecular organization unit rDNA member family, Litchi chinensis. Methods. PCR amplification, cloning and sequencing rDNA. Results. It was fo...

31 We examined chromosomal distribution of major ribosomal DNAs (rDNAs), clustered in the nucleolar 32 organizer regions (NORs), in 18 species of moths and butterflies using fluorescence in situ 33 hybridization (FISH) with a codling moth (Cydia pomonella) 18S rDNA probe. Most species showed 34 one or two rDNA clusters in their haploid karyotype but exceptions with four to eleven clusters also ...

Approximately 35% of the human genome can be identified as sequence devoid of a selected-effect function, and not derived from transposable elements or repeated sequences. We provide evidence supporting a known origin for a fraction of this sequence. We show that: 1) highly degraded, but near full length, ribosomal DNA (rDNA) units, including both 45S and Intergenic Spacer (IGS), can be found a...