and is considered a complete strand. Second, the other strand has a short

RNA at the 5’ end, making it an incomplete strand. Hence, one strand

being complete and the other being incomplete, they have a gapped DNA

genome. The mechanism followed by the members of this group must

consider the facts that the 1) transcription occurs in the host nucleus, 2)

only the RNA part would be exported out of the nucleus, and 3) viral

assembly occurs in the host cytoplasm.

Therefore, the gapped genome is first repaired/filled by viral polymerase forming a

circular DNA. This DNA is transcribed into RNA by host polymerase. The RNA

goes out of the nucleus. Finally, the viral RT enzyme makes DNA from RNA,

making it possible to be packaged into virion capsid.

Example: Hepatitis B (Figure 2.3).

2.3

VIRAL INFECTION CYCLE

The viral genome, despite its limited size, will have to follow the general rule of the

“Central Dogma” to transfer the information from its genes to the proteins. The viral

genome needs to first replicate itself. Second, it must transcribe to form a functional

mRNA, and third, this mRNA must undergo translation to generate a functional

protein, including all post-translational modifications, producing an infectious virion,

and for all these it depends on the host system. An infection cycle needs to follow a

series of events ultimately leading to the production of new virions using the host

cellular machinery. There are three types of commonly known infection cycles.

2.3.1

LYTIC CYCLE

A lytic cycle is also known as virulent infection. This type of infection cycle is mostly

followed by viruses infecting bacteria (bacteriophages, Figure 2.4). This cycle results

FIGURE 2.4 Bacteriophage: A virus that infects bacteria.

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Bioprocessing of Viral Vaccines