Involved in transcriptome surveillance. Required for piwi-interacting RNAs (piRNAs) 3'-end trimming, which is important for both fertility and piRNA-directed gene silencing. Has 3' to 5' exonuclease activity in vitro. Co-localizes with prg-1 in germline nuage structures called P granules. Expressed in germline cells. Expressed at low levels at the L1 to L3 larval stages, but begins to accumulate at the L4 stage and reaches its highest expression level at the gravid adult stage. Slight changes of mRNA bulk poly(A) tail lengths (PubMed:23843623). Animals display a reduced brood size at elevated temperature of 25 degrees Celsius compared to wild-type (PubMed:23843623, PubMed:26919432). Accumulation of untrimmed piRNAs with 3' extensions, which are stable and able to co-localize with the piwi protein prg-1. However, while the expression levels of piRNAs remain unchanged, the piwi-dependent mRNA silencing is reduced, as is the production of piwi-dependent secondary small interfering RNAs (siRNAs), also called 22G-RNAs, on mRNA targets. 5'-end processing and methylation of 3'-ends are unaffected. No changes in length distribution of other small RNA species, such as microRNAs (miRNAs) (PubMed:26919432). Belongs to the CAF1 family.