The sequences coding for ribosomal RNAs are present as rDNA repeating units distributed on chromosomes 12, 15, 16, 18 and 19. A 45S rRNA, which serves as the precursor for the 18S, 5.8S and 28S rRNA, is transcribed from each rDNA unit by RNA polymerase I. The number of rDNA repeating units varies between individuals and from chromosome to chromosom...
The sequences coding for ribosomal RNAs are present as rDNA repeating units distributed on chromosomes 12, 15, 16, 18 and 19. A 45S rRNA, which serves as the precursor for the 18S, 5.8S and 28S rRNA, is transcribed from each rDNA unit by RNA polymerase I. The number of rDNA repeating units varies between individuals and from chromosome to chromosome, although usually 30 to 40 repeats are found on each chromosome. These rDNA repeats are not currently annotated on the reference genome. This gene represents the portion of one rDNA repeat which encodes a 18S rRNA.