Endonuclease

Function

Endonuclease (ENN) cleaves phosphodiester bond within polynucleotide chain. ENN cleaves DNA at a restriction site which is usually a 6-nucleotide palindrome. ENN is restriction site–specific. Various types of ENN differ by their mechanism of action. ENN is used in genetic engineering to make recombinant DNA. ENN requires a restriction site and a cleavage pattern. ENN-I operates on DNA with separate restriction site and cleavage pattern, while ENN-II operates on overlapping restriction site and cleavage pattern. Some ENNs are encoded within introns thus facilitating their mobility. These ENNs or inteins are designated I-ENN^[1].
The Cas ENN proteins are part of CRISPR/Cas prokaryotic immune system which confers protection from foreign genetic elements like viruses. The CRISPR (Clustered Regularly Interspersed Short Palindromic Repeats) are DNA loci which are found in ca. 40% of the bacteria. The CRISPR/Cas system is being used lately as gene editing tool^[2]. For more details see

• CRISPR-Cas
  
• CRISPR-Cas Part II
  
• Cas9
  
• CRISPR-Cas9
  
• CRISPR type I-E (Cascade)
  
• CRISPR type V
  
• CRISPR subtype I-B
  
• CRISPR subtype I-C
  
• CRISPR subtype I-F
  
• CRISPR subtype III-A (Csm complex)
  
• CRISPR subtype III-B (Cmr complex)
  

Intron-encoded ENN or homing ENN are encoded by genes with mobile, self-splicing introns. They promote the movement of DNA sequences from one chromosome location to another^[3].
See also

• Apurinic-Apyrimidinic Endonuclease-1
  
• For EcoRV ENN see Student Projects for UMass Chemistry 423 Spring 2012-3
  
• For NEI ENN see DNA repair protein human endonuclease VIII-like 1 (NEIL1).

Relevance

Sickle cell anemia is caused by mutation in the recognition site of MstII ENN.

Disease

Mutation in UV-specific ENN causes Xeroderma pigmentosa. Mutations in tRNA-splicing ENN cause pontocerebellar hypoplasia.

Structural highlights

(PDB code 1rva).