S1 domain

{{Infobox protein family

| Symbol = S1

| Name = S1 domain

| image = PDB_1sn8_EBI.jpg

| caption = Crystal structure of the S1 domain of RNase E from E. coli (Pb derivative).{{cite journal |author=Schubert M |title=Structural characterization of the RNase E S1 domain and identification of its oligonucleotide-binding and dimerization interfaces |journal=J. Mol. Biol. |volume=341 |issue=1 |pages=37–54 |date=July 2004 |pmid=15312761 |doi=10.1016/j.jmb.2004.05.061 |name-list-style=vanc|author2=Edge RE |author3=Lario P |display-authors=3 |last4=Cook |first4=Michael A. |last5=Strynadka |first5=Natalie C.J. |last6=MacKie |first6=George A. |last7=McIntosh |first7=Lawrence P.|citeseerx=10.1.1.513.8431 }}

| SMART = S1

| OPM family =

| OPM protein =

| PDB = {{PDB2|1sn8}}

| Pfam = PF00575

| Pfam_clan = CL0021

| InterPro = IPR003029

| PROSITE = PDOC00053

| MEROPS = S15

| SCOP = 1sro

| TCDB =

| CAZy =

| CDD = cd00164

}}

The S1 domain is a protein domain that was originally identified in ribosomal protein S1 but is found in a large number of RNA-associated proteins. The structure of the S1 RNA-binding domain from the Escherichia coli polynucleotide phosphorylase has been determined using NMR methods and consists of a five-stranded antiparallel beta barrel. Conserved residues on one face of the barrel and adjacent loops form the putative RNA-binding site.{{cite journal |vauthors=Bycroft M, Hubbard TJ, Proctor M, Freund SM, Murzin AG |title=The solution structure of the S1 RNA binding domain: a member of an ancient nucleic acid-binding fold |journal=Cell |volume=88 |issue=2 |pages=235–42 |date=January 1997 |pmid=9008164 |doi= 10.1016/S0092-8674(00)81844-9|s2cid=9623142 |doi-access=free }}

The structure of the S1 domain is very similar to that of cold shock proteins. This suggests that they may both be derived from an ancient nucleic acid-binding protein.