Bacteriophages use different mechanisms for host cell infection and viral replication. During the lytic replication pathway, bacteriophages infect the host bacterial cells and immediately build new virions. During which of the key steps is the genome packed into capsid and phage structures put together?

Assembly

Explanation:

But why assembly?

While Assembly is happening, all parts of the bacteriophage are replicated and their viral factors fill the viral genome into the capsid, meanwhile, they are still some phage parts being assembled. The bacteriophage basically add their genomes into a capsid as an extra to the assembly process, while the phage is being put together.

We also have the replication step, but during this time, when the viral genome is inside, there is no genome packing, instead, the bacteriophage takes control of the host cells factors and makes them transcribe and translate viral genes.

Another step would be penetration, but here, the bacteriophage is injecting its genetic material into the cells structure by bypassing the cell's wall and plasma membrane, but there is no genome packing, since the capsid remains empty and outside the cell.

Last but not least would be the release step, in which the bacteriophages use an enzyme called lysozyme, which erodes the host cell walls and causes it to burst, once the assembled phages are mature (thus the genome packing would be over) releasing other bacteriophages to infect surrounding cells.