Alu RNA regulates the cellular pool of active ribosomes by targeted delivery of SRP9/14 to 40S subunits

Ivanova, Elena; Berger, Audrey; Scherrer, Anne; Alkalaeva, Elena; Strub, Katharina

So far, we used uncapped mRNAs in the experiments. However, translation of mRNAs in vivo usually depends on the cap structure. In addition, most translation regulators affect mRNA recruitment to the 43S complex by interacting with the 5 or 3 UTR of the mRNA. To investigate whether the cap structure and the 5 UTR affect the inhibitory activity of Alu RNPs, we generated reporter constructs in which the Firefly luciferase coding sequence (Fluc) was fused to the 5 UTRs of the ␤-globin (␤-glo), ␤-actin (␤-act) and LINE-1 (L1) mRNAs. The ␤-glo and ␤-act mRNAs have relatively short 5 UTRs (53 and 84 nucleotides, respectively) while the L1 5 UTR is GC-rich and 900 nucleotides in length. Uncapped and capped transcripts of the three reporter con- structs were translated in RRL in the presence of AluY A and scAluY A RNPs. Translation efficiencies were not significantly different between the capped and uncapped transcripts and between the reporter mRNAs comprising different 5 UTRs ( Figure 4A ). They were reduced by 40-60% in the presence of both Alu RNPs ( Figure 4A ). Hence, Alu RNPs can inhibit cap-dependent translation of mRNAs with different 5 UTRs.