Virus Transduction and Integration

Some viruses produce a small proportion of viruses that contain host DNA in addition to or instead of viral DNA. These virions are able to transfer host genes from one cell to another. In bacteriophages, during the process called transduction, these genes can be incorporated into the recipient cell’s chromosome, thus effecting genetic recombination.

Integration

Many viruses also interact with the host cell in such a way that the viral DNA, instead of replicating independently within the host cell, is integrated into the host cell DNA. It is then replicated and passed on to daughter cells, as are the host cell’s genes. Single or multiple copies of part or all of the viral DNA infecting animals may be incorporated into the host cell DNA. When the viral DNA is integrated, virions are not produced and the host cell is not killed. When a complete copy of viral DNA is present, the cell may return at some time to a lytic mode of virus replication with subsequent production of new virions.

RNA as Genetic Material

The RNA containing viruses are unique living system because they use RNA as their primary genetic material. Some RNA containing viruses produce enzymes that are capable of making new copies of RNA directly from the original molecule, thus circumventing DNA entirely. Retroviruses produce the enzyme called RNA-directed DNA polymerase, or reverse transcriptase, which can make a DNA molecule from the RNA molecule. This DNA formed from RNA then serves as the principal genetic molecule within the infected cell.