Packaging of genome in virus particle- Virus genome is packed in a nucleoprotein complex to give virus particle. These virus particles bind to the host cells and deliver the genome for further replication. The steps in packaging are given in Figure 18.2. Phage genome is replicated by a rolling circle model to produce long genome where cos sites are present on regular interval. The 2 flanking cos sites and the DNA in between them constitute one virus genome or monomeric unit. In the presence of head precursor, the long genome is cleaved into the monomeric unit and encapsulated. Nicks are introduced on both strands of the genome to generate a linear strand that serves as a cohesive site to facilitate circularization in host cell.  

Figure 18.2: Packaging Mechanism of bacteriophage λ