In addition, evidence for a direct interaction of the PK loop 1 (L1) with the 3′ end of the genome and with nsp8 and nsp9 has been reported. Based of these studies, a model for the initiation of coronavirus negative-strand RNA synthesis was proposed. In this model,  the binding of  a protein complex (including nsp8 and nsp9) to the stem formed by base-pairing of the PK L1 and the 3′ end of the genome may cause a conformational shift that leaves free the 3′ end of the genome and disrupts the lower stem of the BSL, leading to the formation of the PK.