= 5S ribosomal RNA
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<5S ribosomal RNA> is a small, roughly 120-<nucleotide> <ribosomal RNA> of the large subunit of cytoplasmic <ribosomes>. Its folded <RNA> contributes to the central protuberance, together with <ribosomal proteins> and parts of the larger <ribosomal RNA>. In bacterial <ribosomes>, it associates with the 50S subunit. The name refers to a <sedimentation coefficient>, not a count of five bases. Its conserved fold contains five helices and five loops.<Ribosome engineering reveals the importance of 5S rRNA autonomy for ribosome assembly by Shijie Huang and others>[Introduction and Figure 1: 120-nucleotide RNA, secondary structure and E. coli large-subunit location]{ref}
The role of a component can be tested by changing its physical independence. In a 2020 <experiment>, researchers joined a rearranged 5S sequence to the much larger 23S <ribosomal RNA> and removed the ordinary free 5S copies from <Escherichia coli>. Some engineered cells survived and their properly assembled <ribosomes> remained active in <translation>. However, defective large subunits accumulated. <Cryo-electron microscopy> showed malformed regions of the catalytic center in these misassembled particles.<Ribosome engineering reveals the importance of 5S rRNA autonomy for ribosome assembly by Shijie Huang and others>[Results: Generating a bacterial strain devoid of free 5S rRNA; Figures 3 and 6–7]{ref} Survival therefore distinguishes the need for the 5S sequence from the need to keep it as a separate <RNA>; it does not establish that assembly is unaffected.
In eukaryotes, 5S <ribosomal RNA> is transcribed by <RNA polymerase III>, unlike the major precursor transcribed by <RNA polymerase I>. The 1974 polymerase study identified the polymerase-III association through distinct inhibition responses of <RNA> synthesis in isolated nuclei and separated enzyme preparations.<Role of DNA-Dependent RNA Polymerase III in the Transcription of the tRNA and 5S RNA Genes by Roberto Weinmann and Robert G. Roeder>[Abstract: alpha-amanitin inhibition distinguishes synthesis of 5S and larger ribosomal RNAs]{ref}
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