Ribonuclease (RNase) degrades RNA. The endonucleases cleave single or double stranded RNA and include RNase III, A, T1 H and P. Exo-RNases remove terminal nucleotide from the ends of the RNA molecule. They include RNase II D, T, PH, Polynucleotide Phosphorylase (PNPase) and oligoribonuclease (ORNase).
- RNase A cleaves C or U of single-stranded RNA (ssRNA).
- RNase BA is RNase from Bacillus amyloliquefaciens.
- RNase D degrades 3'-end pre-tRNA.
- RNase H cleaves RNA/DNA double-strand to produce ssDNA.
- RNase I cleaves 3'-end of ssRNA.
- RNase II degrades 3'-end ssRNA.
- RNase III cleaves rRNA.
- RNase 5 is known as angiogenin and is a potent stimulator of new blood vessels formation.
- RNase P is a ribozyme.
- RNase S is RNase A cleaved by subtilisin.
- RNase SA is RNase from Streptomyces auerofaciens.
- RNase T is involved in RNA maturation.
- RNase T1 cleaves 3'-end G from ssRNA.
- RNase U2 cleaves 3'-end A from ssRNA.
- α-sarcin is a cytotoxic RNase which cleaves a phosphodiester bond in a conserved rRNA loop and inactivates the ribosome.
- oligoribonuclease is an exoribonuclease which cleaves 3'-end of viral RNA-DNA hybrid.
- Polynucleotide phosphorylase is a bifunctional enzyme which has exoribonuclease activity.
- Binase is a microbial RNase which cleaves endonucleolyticly ssRNA.
- Poly(A)-specific RNase cleaves exonucleolyticly the poly(A) tail.
For more details on RNase A see:
For RNase B and RNase S see RNaseS RNaseB.
Active Site of Ribonuclease A
Ribonuclease A cleaves RNA strands by catalyzing a transphosphorylation reaction where the 2'-OH of the ribose sugar attacks the neighboring phosphate, releasing the ribose on the the other side of the phosphate. This structure shows ribonuclease A (in blue) bound to short DNA strand composed of four thymidines (in pink). Ribonuclease binds tightly to DNA, but since DNA is missing the 2'-OH, ribonuclease does not cleave it. are shown that are important for catalysis. The 3' carbon on the DNA is shown in red--it is the site where the 2'-OH is connected in RNA. The two histidines perform the proton transfers that are needed in the reaction, and the lysine stabilizes the intermediate that is formed as the 2'-OH attacks the phosphate. Ribonuclease cleaves RNA strands best next to cytidine and uridine nucleotides--the reason for this may be seen in a . Notice that the small pyrimidine base is surrounded by protein atoms. A larger purine base would not fit well in this space.[1]
