Page 251 - Review of Medical Microbiology and Immunology ( PDFDrive )

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PART III Basic Virology
240
Viral antigens
on cell membrane
cell result. One correlate of the lysogenic state is that the
repressor can also prevent the replication of additional
lambda phages that infect subsequently. This is called
Nucleocapsid
“immunity” and is specifically directed against lambda
Budding
Protein coat
virion
(capsid)
in lambda DNA; other phages are not affected.
The next important step in the lysogenic cycle is the
Nucleic Envelope phage because the repressor binds only to the operator sites
integration of the viral DNA into the cell DNA. This
acid core Mature virion occurs by the matching of a specific attachment site on the
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lambda DNA to a homologous site on the E. coli DNA and
the integration (breakage and rejoining) of the two DNAs
FIGURE 29–5
Budding. Most enveloped viruses derive their
integrated viral DNA is called a prophage. Most lysogenic
lipoprotein envelope from the cell membrane. The matrix protein
phages integrate at one or a few specific sites, but some,
mediates the interaction between the viral nucleocapsid and the
such as the Mu (or mutator) phage, can integrate their
viral envelope. (Reproduced with permission from Mims CA. The Pathogenesis of
Infectious Disease. 3rd ed, Academic Press. Copyright 1987 Elsevier.)
λ Bacteriophage
infects E. coli
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Lysogenic cycle
Lytic cycle
Choice
Prophage

λ-Phage DNA
of many
integrates into
progeny
E. coli DNA
λ phage
and no progeny
phage are made
at this time
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UV irradiation
Release of
and lysis
λ-Phage DNA
of E. coli
excised from
integrated state
and λ phage
synthesized

Release of
λ phage
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and lysis
of E. coli
FIGURE 29–6
Comparison of the lytic and lysogenic cycles of bacteriophage (phage) replication. In the lytic cycle, replication of the
phage is completed without interruption. In the lysogenic cycle, replication of the phage is interrupted, and the phage DNA integrates into the
bacterial DNA. The integrated DNA is called a prophage and can remain in the integrated state for long periods. If the bacteria are exposed to
certain activators such as ultraviolet (UV) light, the prophage DNA is excised from the bacterial DNA and the phage enters the lytic cycle, which
ends with the production of progeny phage.

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