Experimental setup.

<p><b>A,</b> Each member of the miR-34 family is transfected individually into HeLa cells in light SILAC medium. In parallel, a mock transfected control sample is prepared for each member. After 8h of transfection the samples are transferred to different SILAC medium, heavy (“H”) for the control and medium-heavy (“M”) for the miRNA transfected cells. After 24h of pulse labeling corresponding sample are combined and processed for mass spectrometry. The resulting peaks for one peptide are shown as an example. Peptides produced before pulse labeling appear as light peaks and can be disregarded. Differences in protein synthesis between control and miRNA-transfected samples can be read from the H/M ratio of the respective peptides. <b>B</b>, Nucleotide sequences of the miR-34 family members miR-34a and miR-34c. To investigate the importance of 5′ versus 3′ends two miRNA chimeras were constructed swapping head (nt 1-9) and tail of miR-34a and miR-34c respectively. Differences in the nucleotide sequence are marked in blue. The seed is labeled red.