The gene that produces the precursor RNA transcript to the three largest structural rRNA molecules (rDNA) is present in multiple copies and organized into gene clusters. The 10 human rDNA clusters represent <0.5% of the diploid human genome but are critically important for cellular viability. Individual genes within rDNA clusters possess very high levels of sequence identity with respect to eac...

Sequencing of the gene coding for 16S rRNA (16S rDNA) is a well-established method used to identify bacteria, particularly mycobacteria. Unique sequences allow identification of a particular genus and species. If more than one 16S rDNA is present on one mycobacterial genome, their sequences are assumed to be strictly or almost identical. We have isolated a slowly growing Mycobacterium strain, "...

BACKGROUND RNA silencing is a common term for pathways utilizing small RNAs as sequence-specific guides to repress gene expression. Components of the RNA silencing machinery are involved in different aspects of chromatin function in numerous organisms. However, association of RNA silencing with chromatin in mammalian cells remains unclear. METHODOLOGY/PRINCIPAL FINDINGS Immunostaining of mito...

Glechoma L. (Lamiaceae) is distributed in eastern Asia and Europe. Understanding chromosome evolution in Glechoma has been strongly hampered by its small chromosomes, constant karyotype and polyploidy. Here phylogenetic patterns and chromosomal variation in Glechoma species are considered, using genome sizes, chromosome mapping of 5S and 35S rDNAs by fluorescence in situ hybridisation (FISH), a...

Aging and longevity are complex traits influenced by genetic and environmental factors. To identify quantitative trait loci (QTLs) that control replicative lifespan, we employed an outbred Saccharomyces cerevisiae model, generated by crossing a vineyard and a laboratory strain. The predominant QTL mapped to the rDNA, with the vineyard rDNA conferring a lifespan increase of 41%. The lifespan ext...

The ribosomal rDNA gene array is an epigenetically-regulated repeated gene locus. While rDNA copy number varies widely between and within species, the functional consequences of subtle copy number polymorphisms have been largely unknown. Deletions in the Drosophila Y-linked rDNA modifies heterochromatin-induced position effect variegation (PEV), but it has been unknown if the euchromatic compon...

The target of rapamycin (TOR) kinase is an evolutionarily conserved key regulator of eukaryotic cell growth and proliferation. Recently, it has been reported that inhibition of TOR signaling pathway can delay aging and extend lifespan in several eukaryotic organisms, but how lifespan extension is mediated by inhibition of TOR signaling is poorly understood. Here we report that rapamycin treatme...

The in vivo formation of covalent aflatoxin B1 (AFB1)-DNA adducts within the rRNA gene sequences of nuclear DNA has been studied in AFB1-treated rats. Liver nuclear DNA, enriched in ribosomal DNA (rDNA) by one round of cesium salt density gradient centrifugation, was treated under buffered alkaline conditions to convert unstable AFB1-N7-guanine adducts to stable AFB1-formamidopyrimidine derivat...

In budding yeast, silent chromatin is defined at the region of telomeres, rDNA loci, and silent mating loci. Although the silent chromatin at different loci shows structural similarity, the underlying mechanism to establish, maintain, and inherit these structures may be fundamentally different. In this study, we found two arginine residues within histone H2B, which are specifically required to ...