5S Ribosomal RNA

5S ribosomal RNA (5S rRNA) is a component of the large ribosomal subunit in both prokaryotes (50S) and eukaryotes (60S). At about 120 nucleotides in length it is quite short compared to other ribosomal RNAs. 5S rRNA is not found in the mitochondrial ribosomes of fungi and animals.

Eukaryotic 5S rRNA is synthesised by RNA polymerase III, whereas most other eukaroytic rRNAs are cleaved from a 45S precursor transcribed by RNA polymerase I. In Xenopus oocytes, it has been shown that fingers 4-7 of the nine-zinc finger transcription factor TFIIIA can bind to the central region of 5S RNA. Binding between 5S rRNA and TFIIIA serves to both repress further transcription of the 5S RNA gene and stabilize the 5S RNA transcript until it is required for ribosome assembly.