HeLa cells were transfected with 100 nM miRNA duplex as described17 (link) and harvested 12 and 32 h later. Haematopoietic progenitors were isolated from wild-type (WT) and mir-223 knockout (KO) male mice and cultured in media containing granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF) as described16 (link) for six days before harvesting. Just before harvesting, translation was arrested using cycloheximide for 8 min at 37 °C. Harvested cells were partitioned into two portions for ribosome profiling and mRNA profiling. Ribosome profiling was performed as outlined in Fig. 1a. For mRNA profiling, poly(A)+ mRNA was randomly fragmented by partial alkaline hydrolysis and size-selected RNA fragments were used to construct libraries for high-throughput sequencing. Illumina sequencing reads were mapped using the Bowtie short-read mapping program32 (link). An iterative mapping strategy was adopted to obtain unique genome-matching and splice junction-spanning reads. A set of non-redundant transcripts served as our reference transcript database, which was used to map splice junction-spanning reads, quantify gene expression, and quantify RPF and mRNA-Seq changes.