This family aligns residues towards the N-terminus of several proteins with multiple functions. The members of this family all appear to possess 5'-3' exonuclease activity EC:3.1.11.-. Thus, the aligned region may be necessary for 5' to 3' exonuclease function. The family also contains several Xrn1 and Xrn2 proteins. The 5'-3' exoribonucleases Xrn1p and Xrn2p/Rat1p function in the degradation and processing of several classes of RNA in Saccharomyces cerevisiae. Xrn1p is the main enzyme catalysing cytoplasmic mRNA degradation in multiple decay pathways, whereas Xrn2p/Rat1p functions in the processing of rRNAs and small nucleolar RNAs (snoRNAs) in the nucleus [3].

1: Requirement of S. pombe exonuclease II, a homologue of S. cerevisiae Sep1, for normal mitotic growth and viability. Szankasi P, Smith GR; Curr Genet 1996;30:284-293. PMID:8781170

2: Identification and developmental expression of a 5'-3' exoribonuclease from Drosophila melanogaster. Till DD, Linz B, Seago JE, Elgar SJ, Marujo PE, Elias ML, Arraiano CM, McClellan JA, McCarthy JE, Newbury SF; Mech Dev 1998;79:51-55. PMID:10349620

3: Novel features of the XRN-family in Arabidopsis: evidence that AtXRN4, one of several orthologs of nuclear Xrn2p/Rat1p, functions in the cytoplasm. Kastenmayer JP, Green PJ; Proc Natl Acad Sci U S A 2000;97:13985-13990. PMID:11106401