Deadenylation is the major step in triggering mRNA decay and results in mRNA 
translation inhibition in eukaryotic cells. Therefore, it is plausible that 
deadenylation also induces the mRNP remodeling required for formation of GW 
bodies or RNA processing bodies (P-bodies), which harbor translationally 
silenced mRNPs. In this chapter, we discuss several examples to illustrate the 
roles of deadenylation in regulating gene expression. We highlight several lines 
of evidence indicating that even though non-translatable mRNPs may be prepared 
and/or assembled into P-bodies in different ways, deadenylation is always a 
necessary, and perhaps the earliest, step in mRNA decay pathways that enable 
mRNP remodeling required for P-body formation. Thus, deadenylation and the 
participating deadenylases are not simply required for preparing mRNA 
substrates; they play an indispensable role both structurally and functionally 
in P-body formation and regulation.