Ribonuclease T1


Ribonuclease T1 is a fungal endonuclease that cleaves single-stranded RNA after guanine residues, i.e., on their 3' end; the most commonly studied form of this enzyme is the version found in the mold Aspergillus oryzae. Owing to its specificity for guanine, RNase T1 is often used to digest denatured RNA prior to sequencing. Similar to other ribonucleases such as barnase and RNase A, ribonuclease T1 has been popular for folding studies.
Structurally, ribonuclease T1 is a small α+β protein with a four-stranded, antiparallel beta sheet covering a long alpha helix. RNase T1 has two disulfide bonds, Cys2-Cys10 and Cys6-Cys103, of which the latter contributes more to its folding stability; complete reduction of both disulfides usually unfolds the protein, although its folding can be rescued with high salt concentrations.
RNase T1 also has four prolines, two of which have cis isomers of their X-Pro peptide bonds. Nonnative isomers of these prolines can retard conformational folding dramatically, folding on a characteristic time scale of 7,000 seconds at 10 °C and pH 5.