library_construction_protocol: Cells were washed twice with cold buffer containing 20 mM Tris pH 8, 140 mM KCl, 5 mM MgCl2 and 100 µg/ml CHX. The cells were collected and lyzed with 500 µl of the same buffer containing 0.5% Triton, 0.5% DOC, 1.5 mM DTT, 150 units RNAse inhibitor (Eurx) and 5 µl of protease inhibitor (Sigma). The lyzed samples were centrifuged at 12,000g at 4˚C for 5 min. The cleared lysates were loaded onto a 10–50% sucrose gradient and centrifuged at 38,000 RPM in an SW41 rotor for 105 min at 4˚C. Gradients were fractionated and the optical density at 254 nm was continuously recorded using the ISCO absorbance detector UA-6. The collected samples were merged to create the fractions: Light polysome (2-5 ribosomes) and Heavy (6+ ribosomes). The RNA of these fractions and the Input samples were isolated using Trizol and Direc-Zol RNA mini-prep kits (Zymo Research). Equivalent RNA concentrations were taken from each fraction for the library preparation for MARS-Seq