sentence: However , given that all NMD targets do not require all the same NMD factors for their degradation ( 34 – 36 ) and some plants have different complements of NMD factors ( 26,33,37 – 39 ) , the study of endogenous NMD targets in xrn4 is warranted.In contrast to NMD , which is often initiated without deadenylation , the first step in current models for the turnover of many mRNAs degraded by XRN1 or XRN4 is deadenylation ( see Figure 1 in 2,3,40 – 42 ) .