Subsequently, a nested set of subgenomic RNAs (sgRNAs) are synthesized by RTC in a manner of discontinuous transcription. These subgenomic messenger RNAs (mRNAs) possess common 5′-leader and 3′-terminal sequences. Transcription termination and subsequent acquisitio nof a leader RNA occurs at transcription regulatory sequences, located between open reading frames(ORFs). These minus-strand sgRNAs serve as the templates for the production of subgenomic mRNAs.