2.5 g total RNA was ligated to an adaptor DNA oligonucleotide using a T4 RNA ligase (New England Biolabs) for 3 hours at 37C. The ligated RNA was isolated by UltraPure (ThermoFisher) phenol, chloroform and alcohol precipitation followed by reverse transcription using the SuperScript III Reverse Transcriptase (Invitrogen) with an anti-adaptor primer. The PCR was performed with Phusion Plus DNA polymerase (Thermo Scientific) using a primer designed to bind the ligated adaptor RNA sequence and a gene-specific primer for each RNA target.