Fig. 1. RT–PCR reveals the long transcripts containing miRNAs. (A) HeLa total RNA was used for reverse transcription using a primer that binds downstream of mir-23∼27∼24-2. The product from the reverse transcription reaction served as the template for PCR to amplify the indicated regions containing the miRNA cluster. As a control, reverse transcriptase was omitted (lane 2). For RNase treatment, DNase-free RNase A (Ambion) was added to a final concentration of 50 µg/ml and incubated at 37°C for 2 min before reverse transcription. The illustration on the right side shows the template miRNA genes, the primers for PCR and the PCR product. Gray and black boxes indicate the regions corresponding to ∼70 nt precursors and mature miRNAs, respectively. (B) A similar experiment as in (A) was performed for mir-17∼18∼19a∼20∼19b-1. (C) A similar experiment as in (A) was performed for mir-30a.