S4 protein domain

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PDB 2qoy EBI.png
Pfam clanCL0492

In molecular biology, S4 domain refers to a small RNA-binding protein domain found in a ribosomal protein named S4. The S4 domain is approximately 60-65 amino acid residues long, occurs in a single copy at various positions in different proteins and was originally found in pseudouridine synthases, a bacterial ribosome-associated protein.[1]

The S4 protein helps to initiate assembly of the 16S rRNA. In this way proteins serve to organise and stabilise the rRNA tertiary structure.[2][3]


The function of the S4 domain is to be an RNA-binding protein. S4 is a multifunctional protein, and it must bind to the 16S ribosomal RNA. In addition, the S4 domain binds a complex pseudoknot and represses translation. More specifically, this protein domain delivers nucleotide-modifying enzymes to RNA and to regulates translation through structure specific RNA binding.[1]


The S4 protein domain is composed of three alpha helices and five beta strands. It is organized as an antiparallel sheet in a Greek key motif.[4]


  1. ^ a b Aravind L, Koonin EV (March 1999). "Novel predicted RNA-binding domains associated with the translation machinery" (PDF). J. Mol. Evol. 48 (3): 291–302. doi:10.1007/pl00006472. PMID 10093218.
  2. ^ Maguire BA, Zimmermann RA (March 2001). "The ribosome in focus". Cell. 104 (6): 813–6. doi:10.1016/s0092-8674(01)00278-1. PMID 11290319.
  3. ^ Chandra Sanyal S, Liljas A (December 2000). "The end of the beginning: structural studies of ribosomal proteins". Curr. Opin. Struct. Biol. 10 (6): 633–6. doi:10.1016/S0959-440X(00)00143-3. PMID 11114498.
  4. ^ Davies C, Gerstner RB, Draper DE, Ramakrishnan V, White SW (1998). "The crystal structure of ribosomal protein S4 reveals a two-domain molecule with an extensive RNA-binding surface: one domain shows structural homology to the ETS DNA-binding motif". EMBO J. 17 (16): 4545–58. doi:10.1093/emboj/17.16.4545. PMC 1170785. PMID 9707415.
This article incorporates text from the public domain Pfam and InterPro: IPR002942