Bacterial pellet from log-phase cultures of M. tuberculosis and M. smegmatis were resuspended in TRIzol reagent (Invitrogen) and immediately transferred to 2 ml screw-cap tubes containing 0.1 mm zirconia/silica beads (BioSpec Products). M. tuberculosis cells were lysed using a FastPrep-24 bead-beater (MP Biomedicals) 3 times for 30 seconds each at speed 6. M. smegmatis cells were lysed using MagNalyser (Roche). Samples were kept on ice for 1 min between pulses. The TRIzol extracted RNA was treated twice with DNAse and further purified using RNAeasy kit (Qiagen).