FIGURE 2.

Interactions between RNA binding proteins and the CCR4–NOT complex in germ cells (A) and early embryos (B). Black lines represent mRNAs, gray boxes are coding sequences, white boxes are binding motifs for specific RNA binding proteins [NRE, nanos response element bound by Pumilio (Pum); SRE, Smaug recognition element]. The CCR4–NOT complex is in green. CCR4 is shown degrading the poly(A) tail, but the division of labor between POP2 and CCR4 remains to be analyzed. (A) PGCs, primordial germ cells; GSCs, germline stem cells. In contrast to most other examples, the Bicaudal-C (Bic-C) binding element is localized in the 5′ UTR in Bic-C mRNA (Chicoine et al., 2007). (B) The red comb represent piRNAs. The interaction between Smaug and POP2 is suggested from co-immunoprecipitation assays, but has not been verified in vitro. Me31B and Trailer Hitch (Tral) are translational repressors interacting with Cup, which are found in both SRE binding complexes (Jeske et al., 2011) and NOT1 interacting proteins (Temme et al., 2010) in embryo extracts. A direct interaction between the human homolog of Me31B and NOT1 has recently been reported (Chen et al. 2014a; Mathys et al. 2014). A role of Me31B and Tral in Smaug-dependent deadenylation has not been investigated.