The location of NORs and the nucleolar cycle in human cells.
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.[1] These regions code for 5.8S, 18S, and 28S ribosomal RNA.[1] The NORs are "sandwiched" between the repetitive, heterochromatic DNA sequences of the centromeres and telomeres.[1] The exact sequence of these regions is not included in the human reference genome as of 2016[1] or the GRCh38.p10 released January 6, 2017.[2] 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.[3] However, it is known that NORs contain tandem copies of ribosomal DNA (rDNA) genes.[1] Some sequences of flanking sequences proximal and distal to NORs have been reported.[4] The NORs of a loris have been reported to be highly variable.[5] There are also DNA sequences related to rDNA that are on other chromosomes and may be involved in nucleoli formation.[6]
Silver-stained nucleolus organizer region (arrow) at the tip of a chromosome of the Gecko Lepidodactylus lugubris
^The Genome Reference Consortium. "GRCh38.p13 has been released". GenomeRef. Retrieved 16 August 2019.
^Floutsakou I, Agrawal S, Nguyen TT, Seoighe C, Ganley AR, McStay B (2013). "The shared genomic architecture of human nucleolar organizer regions". Genome Research. 23 (12): 2003–12. doi:10.1101/gr.157941.113. PMC 3847771. PMID 23990606.
^Baicharoen S, Hirai Y, Srikulnath K, Kongprom U, Hirai H (2016). "Hypervariability of Nucleolus Organizer Regions in Bengal Slow Lorises, Nycticebus bengalensis (Primates, Lorisidae)". Cytogenetic and Genome Research. 149 (4): 267–273. doi:10.1159/000449145. PMID 27648559.
^Kupriyanova NS, Netchvolodov KK, Sadova AA, Cherepanova MD, Ryskov AP (2015). "Non-canonical ribosomal DNA segments in the human genome, and nucleoli functioning". Gene. 572 (2): 237–42. doi:10.1016/j.gene.2015.07.019. PMID 26164756.
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nucleolar organizer regions (NOR). The main roles of the nucleolus are to synthesize rRNA and assemble ribosomes. The structural cohesion of the nucleolus depends...
whose secondary constriction is associated with the formation of the nucleolus are referred to as nucleolar SAT-chromosomes. There are at least 4 SAT-chromosomes...
constrictions indicate sites of nucleolus formation and are called "nucleolar organizing regions" (NORs). The nucleolus in the nucleus remains associated...
also called nucleolusorganizer regions, as they give rise to the nucleolus. In rDNA, the tandem repeats are mostly found in the nucleolus; but heterochromatic...
Gene: RNR1 RNA, ribosomal 1". Nucleolusorganizer regions are chromosomal regions crucial for the formation of the nucleolus, located on the short arms of...
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some protein coding genes, human acrocentric p-arms also contain Nucleolusorganizer regions (NORs), from which ribosomal RNA is transcribed. However...
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segregates the DNA from the cytoplasm, disintegrates into small vesicles. The nucleolus, which makes ribosomes in the cell, also disappears. Microtubules project...
is expected to be targeted in the nucleus, specifically the nucleolus. The promoter region is predicted to start 1,303 bp upstream from the 5' UTR and...
B23.1 and B23.2 respectively in rat. The isoform 1 is localized to the nucleolus as is reported for rat B23.1 whereas the isoform 3 (B23.2) is nucleoplasmic...
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