Related Research Articles
Ribosomal DNA (rDNA) is a DNA sequence that codes for ribosomal RNA. These sequences regulate transcription initiation and amplification, and contain both transcribed and non-transcribed spacer segments. The rRNA transcribed from the approximately 600 rDNA repeats forms the most abundant section of RNA found in cells of eukaryotes. Ribosomes are assemblies of proteins and rRNA molecules that translate mRNA molecules to produce proteins. As shown in the figure, rDNA of eukaryotes consists of a tandem repeat of a unit segment, composed of NTS, ETS, 18S, ITS1, 5.8S, ITS2, and 28S tracts. rDNA has another gene, coding for 5S rRNA, located in the genome in most eukaryotes. 5S rDNA is also present in tandem repeats as in Drosophila. DNA regions that are repetitive often undergo recombination events. The rDNA repeats have many regulatory mechanisms that keep the DNA from undergoing mutations, thus keeping the rDNA conserved.
Nucleolus organizer regions (NORs) are chromosomal regions crucial for the formation of the nucleolus. In humans, the NORs are located on the short arms of the acrocentric chromosomes 13, 14, 15, 21 and 22, the genes RNR1, RNR2, RNR3, RNR4, and RNR5 respectively. These regions code for 5.8S, 18S, and 28S ribosomal RNA. The NORs are "sandwiched" between the repetitive, heterochromatic DNA sequences of the centromeres and telomeres. The exact sequence of these regions is not included in the human reference genome as of 2016 or the GRCh38.p10 released January 6, 2017. On 28 February 2019, GRCh38.p13 was released, which added the NOR sequences for the short arms of chromosomes 13, 14, 15, 21, and 22. However, it is known that NORs contain tandem copies of ribosomal DNA (rDNA) genes. Some sequences of flanking sequences proximal and distal to NORs have been reported. The NORs of a loris have been reported to be highly variable. There are also DNA sequences related to rDNA that are on other chromosomes and may be involved in nucleoli formation.
Nucleolar transcription factor 1 is a protein that in humans is encoded by the UBTF gene.
60S ribosomal protein L7a is a protein that in humans is encoded by the RPL7A gene.
40S ribosomal protein S4, X isoform is a protein that in humans is encoded by the RPS4X gene.
Pescadillo homolog is a protein that in humans is encoded by the PES1 gene.
Nucleolar protein 56 is a protein that in humans is encoded by the NOP56 gene.
3'-5' exoribonuclease CSL4 homolog is an enzyme that in humans is encoded by the EXOSC1 gene.
Probable ATP-dependent RNA helicase DDX56 is an enzyme that in humans is encoded by the DDX56 gene.
RNA, ribosomal 4, also known as RNR4, is a human gene.
40S ribosomal protein S8 is a protein that in humans is encoded by the RPS8 gene.
Ribosomal RNA processing protein 1 homolog A is a protein that in humans is encoded by the RRP1 gene.
RNA, ribosomal 3, also known as RNR3, is a human gene. It is a minor isoform of large subunit of ribonucleotide-diphosphate reductase; the RNR complex catalyzes rate-limiting step in dNTP synthesis, regulated by DNA replication and DNA damage checkpoint pathways via localization of small subunits; RNR3 has a paralog, RNR1, that arose from the whole genome duplication.
RNA, ribosomal 5, also known as RNR5, is a human gene. Genes for ribosomal RNA are clustered on the short arms of chromosomes 13, 14, 15, 20, 21. The gene for RNR5 exists in multiple copies on chromosome 22. Each gene cluster contains 30–40 copies and encodes a 45S RNA product that is then cleaved to form 18S, 5.8S and 28S rRNA subunits. In general, genes for RNA remain poorly annotated in most large public databases.
28S ribosomal protein S28, mitochondrial is a protein that in humans is encoded by the MRPS28 gene.
28S ribosomal protein S24, mitochondrial is a protein that in humans is encoded by the MRPS24 gene.
Probable ribosome biogenesis protein RLP24 is a protein that in humans is encoded by the RSL24D1 gene.
39S ribosomal protein L24, mitochondrial is a protein that in humans is encoded by the MRPL24 gene.
Ribosomal RNA-processing protein 8 is a protein that in humans is encoded by the RRP8 gene.
RRP15-like protein is a protein that in humans is encoded by the RRP15 gene.
References
- ↑ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ↑ "Entrez Gene: RNR1 RNA, ribosomal 1".
