This superfamily entry consists of the ribosomal protein L20 found in the large subunit (50S) of the eubacterial, mitochondrial and plastid ribosome. The N-terminal domain of L20 is unstructured, whereas the C-terminal domain is globular, alpha-helical and is involved in RNA recognition. In the bacterial cytoplasm, L20 can exist in 2 forms - a ribosome-bound state or in a free state. Unbound, L20 is able to associate with its own messenger RNA and exert its regulatory role. This free L20 structure differs from the ribosome-bound L20 crystal structure, the most striking difference being the N-terminal domain, which forms contacts with 23 S rRNA in the ribosome-bound state.

L20 has been shown to partially unfold in the absence of RNA, in regions corresponding to the RNA-binding sites. L20 is involved in the early assembly steps of the 50S subunit and in the feedback control of its own gene. L20 acts as a translational repressor by the binding to its own mRNA, folding into a pseudoknot structure. This dual function involves specific interactions with either the 23 S rRNA or its mRNA.

INTERPRO:IPR035566, PFAM:PF00453,PMID:12368106,PMID:16977336