Ribonuclease T₁ (, ''guanyloribonuclease'', ''Aspergillus oryzae ribonuclease'', ''RNase N1'', ''RNase N2'', ''ribonuclease N3'', ''ribonuclease U1'', ''ribonuclease F1'', ''ribonuclease Ch'', ''ribonuclease PP1'', ''ribonuclease SA'', ''RNase F1'', ''ribonuclease C2'', ''binase'', ''RNase Sa'', ''guanyl-specific RNase'', ''RNase G'', ''RNase T₁'', ''ribonuclease guaninenucleotido-2'-transferase (cyclizing)'', ''ribonuclease N3'', ''ribonuclease N1'') is a

fungal A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

endonuclease Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain. Some, such as deoxyribonuclease I, cut DNA relatively nonspecifically (without regard to sequence), while many, typically called restriction endonucleases ...

that cleaves single-stranded

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

after

guanine Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is called ...

residues, i.e., on their 3' end; the most commonly studied form of this

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

is the version found in the

mold A mold () or mould () is one of the structures certain fungus, fungi can form. The dust-like, colored appearance of molds is due to the formation of Spore#Fungi, spores containing Secondary metabolite#Fungal secondary metabolites, fungal seco ...

Aspergillus oryzae ''Aspergillus oryzae'', also known as , is a filamentous fungus (a mold) used in East Asia to saccharify rice, sweet potato, and barley in the making of alcoholic beverages such as ''sake'' and '' shōchū'', and also to ferment soybeans for m ...

''. Owing to its specificity for guanine, RNase T₁ is often used to digest denatured

prior to sequencing. Similar to other ribonucleases such as

barnase Barnase (a portmanteau of "BActerial" "RiboNucleASE") is a bacterial protein that consists of 110 amino acids and has ribonuclease activity. It is synthesized and secreted by the bacterium '' Bacillus amyloliquefaciens'', but is lethal to the cel ...

and

RNase A Pancreatic ribonuclease family (, ''RNase'', ''RNase I'', ''RNase A'', ''pancreatic RNase'', ''ribonuclease I'', ''endoribonuclease I'', ''ribonucleic phosphatase'', ''alkaline ribonuclease'', ''ribonuclease'', ''gene S glycoproteins'', ''Ceratit ...

, ribonuclease T₁ has been popular for folding studies. Structurally, ribonuclease T₁ is a small α+β protein (104

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s) with a four-stranded, antiparallel

beta sheet The beta sheet, (β-sheet) (also β-pleated sheet) is a common motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a g ...

covering a long

alpha helix The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues e ...

(almost five turns). 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

proline Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the prot ...

s, two of which (Pro39 and Pro55) have ''cis''

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

s of their X-Pro

peptide bond In organic chemistry, a peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide or protein cha ...

s. Nonnative isomers of these prolines can retard conformational folding dramatically, folding on a characteristic time scale of 7,000 seconds (almost two hours) at 10 °C and pH 5.

References

External links

* Ribonucleases {{enzyme-stub