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...

The rDNA cluster in Saccharomyces cerevisiae is located 450 kb from the left end and 610 kb from the right end of chromosome XII and consists of approximately 150 tandemly repeated copies of a 9.1 kb rDNA unit. To explore the biological significance of this specific chromosomal context, chromosome XII was split at both sides of the rDNA cluster and strains harboring deleted variants of chromoso...

Fluorescence in situ hybridization (FISH) technique was used to detect rDNA sites in chickpea and mungbean. In chickpea, the rDNA sites were detected on three pairs of chromosomes. Among these three pairs of chromosomes, one pair exhibited both 25S rDNA and 5S rDNA sites, while in case of other two pairs of chromosomes the 25S rDNA and 5S rDNA sites were located separately on separate pair of c...

Replication of Saccharomyces ribosomal DNA (rDNA) proceeds bidirectionally from origins in a subset of the approximately 150 tandem repeats, but the leftward-moving fork stops when it encounters the replication fork barrier (RFB). The Pif1p helicase and the highly related Rrm3p were rDNA associated in vivo. Both proteins affected rDNA replication but had opposing effects on fork progression. Pi...

P-element transformants of a single rRNA gene (rDNA) were used to investigate the relationship between the organization of the nucleolus organizer (NO) and rDNA function in Drosophila melanogaster. In situ hybridization to rRNA in polytene nuclei of salivary glands demonstrated that an rRNA gene can be transcribed at a high rate when inserted into chromosomal sites other than the NO. Structures...

The recent introduction of molecular techniques in eukaryotic microbial diversity studies, in particular those based in the amplification and sequencing of small-subunit ribosomal DNA (SSU rDNA), has revealed the existence of an unexpected variety of new phylotypes. The taxonomic ascription of the organisms bearing those sequences is generally deduced from phylogenetic analysis. Unfortunately, ...