SL1 and SL2 are conserved in all coronaviruses. SL1 adopts a bipartite structure, and SL2 presents a highly conserved  loop sequence that adopts a YNMG- or CUYG-type tetraloop conformation. Both SLs are required for genome replication, and they may have a specific role in sgmRNA synthesis. SL3, which contains the leader CS, is involved in discontinuous transcription as a receptor for nascent negative-strand RNA.