or lysogenic phage
is a phage
that can exist as a prophage
within its host organism. A prophage is the phage DNA in its dormant state, and is either integrated into the host bacteria
or more rarely exists as a stable plasmid
within the host cell. The prophage expresses gene(s) that repress the phage's lytic
action, and the phage enters the lytic cycle
when this suppression is disrupted. Currently a variety of studies are being conducted to see whether other genes are active during lysogeny, examples of which include phage-encoded tRNA
and virulence genes.
Alternatively, lysogen can refer to a strain of bacterium that carries a prophage.