The 21 nt form produced from the amiR173-21 foldback, however, possessed very low tasiRNA trigger activity, and the few TAS1c-derived siRNA that were produced exhibited no phasing pattern (Fig. 3b, c; Supplementary Fig. 2; Supplementary Table 6).The lack of tasiRNA-trigger activity of miR173-21 could be due to one or more reasons, including failure to associate with AGO1, failure to interact with