P1 is a temperate bacteriophage that infects E. coli. It has an icosahedral head containing linear double-stranded DNA and a contractile tail. The P1 genome is 94 kbp and contains two origins of replication. P1 can exist lysogenically as a plasmid or enter the lytic cycle to produce new phage particles. During lysogeny, P1 DNA circularizes and replicates without integrating into the host genome.

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2. P1 phage

3. AGENDA
01. What is p1 phage
02. Structure
03.Genome
04.The Life Cycle of P1
Phage
05. P1 Transducing
Particles
06. Absorption, Injection
and protection
07. P1 DNA Replication and
Phage Assembly.
08.
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The Location of the P1
Prophage

4. What is p1 phage
P1 is a temperate bacteriophage (phage) that infects Escherichia coli and
a some other bacteria. When undergoing a lysogenic cycle the phage
genome exists as a autonomous plasmid, that is maintained at low copy
number, in the bacterium. It is not integrated in to host genome.

5. Structure
P1 has an icosahedral “head” containing the phage DNA attached to a 220nm long
tube, contractile tail or shealth, and base plate with six tail fibers.
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6. genome
The genome of P1 Phage is linear double stranded DNA Which is
moderately large, about 94 Kbp. The genome is longer, about 120Kbs,
than the actual length when in viral particle as it is created by cutting an
appropriately sized fragment from a concatemeric DNA chain having
multiple copies of the genome. Due to this the ends of the DNA
molecule are identical and are referred to as being “terminally
redundant”. It has large, about 15 kbp, terminal redundancy
The genome contains two origins of replication, oriR which replicates it
during the lysogenic cycle and oriL which replicates it during the lytic
stage. The genome of P1 has 112 protein coding and 5 untranslated
genes. It even encodes 3 of its own tRNAs which are expressed in the
lytic stage.
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7. 7
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phage P1 has two other features that are unusual
among bacteriophage: First, though a temperate phage,
P1 does not integrate its dsDNA genome into the
bacterial genome. Instead, the genome circularizes and
replicates in a plasmid-like state. The phage devotes
several genes to controlling replication and partitioning
of the plasmid so that it is stably maintained at low copy
number.
Second, phage P1 also has two complete sets of tail
fiber genes, each conferring a different host range.
These genes are arranged in opposite orientation in the
phage genome with a single control region located in
between.

8. The Life Cycle of P1 Phage
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Temperate phage, such as P1, have the ability to exist within
the bacterial cell they infect in two different ways. In lysogeny, P1 can exist
within a bacterial cell as a circular DNA in that it exists by replicating as if it
were a plasmid and does not cause cell death. Alternatively, in its lytic phase,
P1 can promote cell lysis during growth resulting in host cell death.
During lysogeny new phage particles are not produced. In contrast, during lytic
growth many new phage particles are assembled and released from the cell. By
alternating between these two modes of infection, P1 can survive during
extreme nutritional conditions that may be imposed upon the bacterial host in
which it exists.

9. The Life Cycle of P1 Phage
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10. • One unusual aspect of P1
development is the formation of
transducing particles or phage
particles that contain
chromosomal DNA instead of
phage DNA.
P1 Transducing
Particles
INFO 1
Absorption, Injection and
protection of the genome
INFO 2
P1 DNA Replication and
Phage Assembly. (Lytic
Cycle)
INFO 3
The Location of the P1
Prophage in a lysogen
(Lysogenic Cycle)
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• The ability to package any
piece of chromosomal DNA
instead of phage DNA makes P1
a generalized transducing gene.

11. Absorption, Injection and protection of the
genome
Once inside the cell, P1 DNA circularizes by homologous
recombination because these DNA when packed it is packed
by Head full Mechanism. This can be done either by host or phage
recombination system
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P1 can contract its tail and inject its DNA into a wide range of
species but cannot replicate in these species.
P1 absorbs to the receptors on the host cells – terminal glucose on the
lipopolysaccharide present on the outer surface of the outer membrane of
the host cell.

12. P1 DNA Replication and Phage Assembly. (Lytic
Cycle)
The P1 plasmid has a separate origin of replication (oriL) that is
activated during the lytic cycle. Like Lambda, early P1 replication
takes place by the theta mode of replication.
Later in infection, P1 switch to rolling circle replication. Rolling circle
replication produces concatemers for packaging into phage heads.
At approx 45 minutes after the infection, the cells are filled with
concatemers of phage DNA, assembled phage heads, and assembled
phage tails. Now complete phage must take place. A protein made
from phage genome recognizes a site on the concatomers of phage
DNA called the pac site.
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13. The Location of the P1 Prophage in a lysogen
(Lysogenic Cycle)
Prophages can be physically located in one or two places in a
lysogen. In case of Lambda, the phage genome is recombined into
the bacterial chromosome. P1 contains an origin for DNA
replication and once the phage genome is converted to circular,
double-stranded DNA, and is maintained in the cytoplasm as a
stably inherited extra-chromosomal piece of DNA or plasmid. In P1,
no integration of DNA, no int/xis System for recombination, So
coordinated DNA replication along with the host DNA occurs.
Coordinated DNA replication occurs, in order to maintain its
population in all daughter cells. If not, when multiplied by binary
fission only one daughter cell will posses the phage DNA and
another daughter cell does not.
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14. https://biotechkhan.wordpress.com/2014/07/08/bacteriophage
-p1-structure-and-life-cycle/
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Reference
• http://web.engr.oregonstate.edu

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