Plays a role in maintenance of steady-state concentration and turnover of microRNAs (miRNA) by degradation of mature miRNA in complex with the exoribonuclease xrn-2 (PubMed:26779609). Stabilizes and enhances the accumulation and activity of the exoribonuclease xrn-2, and thus contributes to miRNA turnover (PubMed:24462208, PubMed:26779609). Interacts (via N-terminus) with xrn-2; the interaction is direct. Ubiquitously expressed throughout development. XTBD domain is necessary for interaction with xrn-2. At 26 degrees Celsius 80% of progeny arrest at the L1 stage of larval development (PubMed:24462208). Reduced xrn-2 levels (PubMed:24462208, PubMed:26779609).