This helical domain is part of the Xrn1 catalytic core [1]. Xrn1 is a cytoplasmic 5'-3' exonuclease that degrades decapped mRNAs.

1: Coupled 5' nucleotide recognition and processivity in Xrn1-mediated mRNA decay. Jinek M, Coyle SM, Doudna JA; Mol Cell. 2011;41:600-608. PMID:21362555

2: Structure and function of the 5'-->3' exoribonuclease Rat1 and its activating partner Rai1. Xiang S, Cooper-Morgan A, Jiao X, Kiledjian M, Manley JL, Tong L; Nature. 2009;458:784-788. PMID:19194460