interferon-stimulated gene 20 kD protein; estrogen-regulated transcript 45 protein; promyelocytic leukemia nuclear body-associated protein ISG20 (ISG20, HEM45)

Function

• exonuclease with specificity for single-stranded RNA
• lesser activity towards DNA (35-fold)
• involved in antiviral function of IFN against RNA viruses
• exonucleolytic cleavage in the 3'- to 5'- direction
• yields nucleoside 5'-phosphates
• component of PML NB complex
  • associates with PML & SP100 in the PML NB complex

Cofactor: Mn+2

Kinetic parameters:

• Optimum pH is 7.0

Structure

belongs to the exonuclease superfamily

Compartment

nucleus

Alternative splicing

named isoforms=2

Expression

• expressed in peripheral blood leukocytes, spleen, thymus, colon, lung
• induced by interferon-alpha & interferon-beta
• weaker induction by interferon-gamma

Pathology

• stable & constitutive expression confers resistance* to
  • vesicular stomatitis virus (VSV)
  • influenza virus
  • encephalomyocarditis virus (EMCV)

* resistance to infection in HeLa cells

• up regulated by E2 in estrogen receptor-positive breast cancer cell lines

More general terms

• exoribonuclease
• nuclear protein

Component of

• PML NB complex

Database

• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=3669
• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:3669
• OMIM: https://mirror.omim.org/entry/604533
• UniProt: http://www.uniprot.org/uniprot/Q96AZ6.html