InterPro domain: IPR027073

This entry includes 5'-3'exoribonuclease type 1 and type 2. Putative viral exonucleases 059L and 012L, plant Xrn3 and Xrn4 also belong to this family. 5'-3'-exoribonucleases are enzymes that degrade RNA by removing terminal nucleotides from the 5' end. An exosome and a 5'-3'-exoribonuclease are important in the degradation of very unstable transcripts [ 1 ].

5'-3'exoribonuclease type 1 (Xrn1, also known as kem1) occurs in animal and fungal lineages. In Saccharomyces cerevisiae, Xrn1 can be activated by Dcs1, a non-essential hydrolase that involved in mRNA decapping. The activation of Xrn1 by Dcs1 is important for respiration [ 2 ].

5'-3' exoribonuclease type 2 (Xrn2, also known as Rat1) occurs in animal, plant and fungal lineages. In Saccharomyces cerevisiae, Rat1 serves to terminateRNA polymerase II (RNAPII) molecules engaged in the production of uncapped RNA [ 3 ].

The concomitant loss of Xrn4 and ABH1/CBP80, a subunit of the mRNA cap binding complex, results in Arabidopsis plants manifesting myriad developmental defects [ 4 ], suggesting that this enzyme is not only important for RNA processing.

1. Control of mRNA degradation in trypanosomes. Biochem. Soc. Trans. 36, 520-1
2. Activation of 5'-3' exoribonuclease Xrn1 by cofactor Dcs1 is essential for mitochondrial function in yeast. Proc. Natl. Acad. Sci. U.S.A. 109, 8264-9
3. The yeast 5'-3' exonuclease Rat1p functions during transcription elongation by RNA polymerase II. Mol. Cell 37, 580-7
4. A link between RNA metabolism and silencing affecting Arabidopsis development. Dev. Cell 14, 854-66