Non-canonical ribosomal DNA segments in the human genome, and nucleoli functioning

Variability of Human rDNA

“…The observed variability, resulting from replication errors or recombination, is most frequently represented by single-nucleotide variants (SNV), short insertions and deletions (indels), as well as variable numbers of the short, repeated elements [74,75]. The potential breakpoints, where DNA sequence tends to undergo these and other changes, are often represented by microsatellites, (TC)n, (TG)n, and short (3-5 bp) poly-N clusters [14,76,77]. Approximately 7.5 variants per kb have been found in rDNA, which is comparable to typical estimates of variation across the genome [61].…”

“…The best studied part of IGS is the ribosomal gene promoter, whose key elements are the upstream control element (UCE) and core promoter elements (CPE) [13]. Upstream of the promoter lies the enhancer, whose precise location in human cells is not established [14,15]. Recent studies suggest that IGS has a complex functional organization.…”

Management of rRNA Transcription Activity in a Human Genome

“…Four stimuli-specific loci producing their own RNAs are currently denoted in the rIGS. They were termed IGS27RNA, IGS22RNA, IGS16RNA, and IGS pRNA [26][27][28]. Functional studies of these molecules have revealed new mechanisms for the regulation of rRNA expression, as well as a novel posttranslation regulatory pathway termed the nucleolar detention pathway.…”

“…The correlation of the fixed 5′-and 3′-ends' number on (NOR)− chromosomes, and their distribution in the IGS27RNA, IGS22RNA, and IGS16RNA areas help to detect local nucleotides in the rIGS that are maximally susceptible to a breakage [28].…”

“…All GenBank accession numbers for IGS27RNA and for IGS22RNA are represented by practically identical sequences. The positions of the fixed 5′-and 3′-ends that are most frequent in the IGS27RNA and IGS22RNA areas are presented by 27,604-27,840 bp and 21,600-21,900 bp, respectively [28].…”