Figure 6. Model of Rrm4‐/Grp1‐mediated endosomal mRNA transport.

1. Schematic drawing of target transcript with Rrm4‐bound regions on top (5′ cap structure, blue circle; 5′ and 3′ UTR, light blue; ORF, dark blue; poly(A) tail, AAAA). Different categories of Rrm4 target transcripts were defined according to the presence of Rrm4 binding sites at the start codon, within the ORF, at the stop codon and in the 3′ UTR. Approximate number of target transcripts and selected examples are given for each category. About 900 of 1,300 target transcripts with an Rrm4 binding site in the ORF harbour an UAUG motif within the ORF binding site. Potential RRM domains of Rrm4 and Grp1 that may mediate RNA binding in the different transcript regions are given in green and magenta, respectively.
2. Simplified model proposing the spatial arrangement of endosomal RBPs with bound target transcripts. The three RRM domains of Rrm4 are schematically displayed and labelled by numbers (FYVE zinc finger domain; PI3P, phosphatidylinositol 3‐phosphate; M, Mademoiselle domain; P and PL, PAM2 and PAM2‐like sequence, respectively; further details, see text). Note that complete endosomal mRNPs will consist of additional mRNA and protein components forming more complex, higher order structures.