Ribonuclease

Function

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 or RNase I endonuclease which cleaves C or U of single-stranded RNA (ssRNA)^[1].
  
• RNase BA is RNase from Bacillus amyloliquefaciens.
  
• RNase D exonuclease which degrades 3'-end pre-tRNA^[2].
  
• RNase H endonuclease which cleaves RNA/DNA double-strand to produce ssDNA^[3].
  
• RNase II exonuclease which degrades 3'-end ssRNA^[4].
  
• RNase III endonuclease which cleaves rRNA.
  
• RNase III Dicer cleaves dsRNA to small interfering RNA and microRNA.
  
• RNase 5 is known as angiogenin and is a potent stimulator of new blood vessels formation.
  
• RNase P endonuclease which is a ribozyme.
  
• RNase S is RNase A cleaved by subtilisin.
  
• RNase SA is RNase from Streptomyces auerofaciens.
  
• RNase T exonuclease which is involved in RNA maturation.
  
• RNase T1 endonuclease which 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 exonuclease which is an exoribonuclease which cleaves 3'-end of viral RNA-DNA hybrid.
  
• Polynucleotide phosphorylase exonuclease which 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:

• RNase A
  
• Ribonuclease A Catalysis
  
• RNase A Oligomers
  
• RNase A NMR
  
• User:R. Jeremy Johnson/RNaseA
  
• RNaseA Nobel Prizes.
  

For RNase B and RNase S see RNaseS RNaseB.

Relevance

The retroviral RNase H inhibitors are investigated as potential antiretroviral (HIV) agents.

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.^[5]