URT and LRT full-length sequences were obtained by amplification of eight overlapping nested PCR products with forward and reverse primers (Table S2) . RT-PCR assays were performed in duplicate to discard any mutations introduced by polymerase errors. We used Platinium Taq DNA Polymerase High Fidelity (Invitrogen) for PCRs, according to the manufacturer's instructions. All amplicons were purified with the microcon columns (Millipore) before sequencing. The eight overlapping PCRs were pooled at equimolar concentrations and used for ultradeep sequencing for each individual sample.