Single-Stranded Filamentous DNA
Bacteriophages M13,f1 and fd
?Distinct Properties of M13
– Infect Escherichia coli
– Infect only male cells through attachment to
the male-specific pilus
– Have circular single-stranded DNA
– Can be used as a cloning vector and DNA
sequencing vehicle in genetic engineering
– Infect but not kill the cells
M13 leaves an infected cell without lysis
Double-Stranded DNA Bacteriophage,the first
discovered phage and the most extensively
studied ds DNA viruses,Example,T7
1,Linear double-stranded DNA with 39,936 base pairs
2,92% DNA codes for protein
3,Gene overlap through translation in different reading
frame and through internal translational
reinitiation as well as internal frame shifts.
4,One of the coded proteins inhibits the host restriction
system,it is synthesized before the entire T7
genome enters the cells.
Genetic
Map of T7
Early transcription occurs
when left end enters cells
A host RNA polymerase
is used just to copy the
first few genes and to
make the mRNA that
codes for the phage-
specific RNA polymerase
Two other early mRNA
code for proteins which
stop the action of host
RNA polymerase
DNA Replication in T7
In both direction,an
RNA primer is involved.
Rightward,RNA primer
is synthesized by T7
RNA polymerase
Leftward,RNA primer is
synthesized by
T7 primase
Both primers are elongated
by T7 DNA polymerase.
DNA Replication in T7
DNA Replication
in T7
?T7 has a much
more complex
replication
scheme than
that seen for the
other bacterial
viruses.
Large Double-Stranded DNA bacteriophages,
the T-even Phages T2,T4 and T6
?T4 (as example)
– 1.7 X 105 base pairs
– Have a unique base,5-hydroxymethylcytosine
instead of cytosine
– The above hydroxyl group is modified by
addition of glucosyl residues
– This glucosylated DNA is resistant to virtually
all restriction endonucleases of the host
DNA replication in T4
Time course of events in phage T4 infection
DNA Replication
in T4
? The cutting enzyme
which forms virus-
sized fragments does
not recognize specific
locations on the long
molecule,but cuts off
DNA irrespective of
the sequence.
? Thus,each virus DNA
sequences at the end of
different molecules are
different.
Temperate Bacterial Viruses,
Lysogeny and Lambda
?Virulent Viruses
?Temperate Viruses
– Lysogeny (溶原性）,Viruses can enter a state
called lysogeny,where most phage genes are
not expressed,and the phage genome is
replicated in synchrony with the host
chromosome
– Prophage or provirus
– Can be induced (lysogenic induction) by UV
radiation,nitrogen mustards or X-ray.
Temperate Bacterial
Viruses,
Lysogeny and
Lambda
Temperate Phage,Lambda
?Linear double-stranded DNA
?Single-stranded tail of 12 nucleotides long
at the 5’-terminus
?These single-stranded ends are
complementary (cohesive)
?The two ends can associate and form a
double-stranded circle containing 48,502
base pairs.
Electron Micrograph of
Lambda particles
Genetic and
Molecular Map
of Lambda
PR,Lytic cycle
PL,Lysogeny
Lytic Growth
of Lambda
?DNA
damage is
caused by
UV,X-ray,
Chemicals
etc.
The
Integration
of lambda
DNA into
the host
chromosome
Lambda Phage
Lambda DNA replication,Circular form (initially)
and Rolling Circle replication (late stage)
Bacterial
Viruses
Main types of
bacterial
viruses.
Sizes are
approximat
e scale
Transposable Phage,Bacteriophage Mu
?Mu,a mutator phage,which has the unusual
property of replicating as a movable genetic
element (a piece of DNA acts as
transposable element)
?Can be used to generate a wide variety of
bacterial mutants very easily
? Three types of transposable elements,
insertion elements,transposons and viruses
like Mu
Transposable Phage,Bacteriophage Mu
?Large double-stranded DNA virus
?39 KB DNA
?Only 37.2 KB is the actual Mu genome,the
rest is host DNA (50-150 base pairs at the left,
1-2 KB at the right end)
?The head of Mu can be filled with foreign
DNA and it brings the foreign genes to other
host cells (transduction)
?Contribute to genetic variation
Bacteriophage
Mu
?Genetic
map of Mu
?Integration
of Mu into
the host
DNA.
Animal Viruses (DNA Viruses)
DNA Viruses
Parvovirus (细小病毒 )
Papovavirus (乳头多
瘤空泡病毒）
Adenovirus （腺病毒）
Iridovirus (虹彩病毒 )
Hepadnavirus (肝炎
DNA病毒）
Poxvirus (天花病毒）
Herpesvirus (疱疹病
毒）
Animal Viruses (RNA Viruses)
小 RNA病毒
呼吸道肠道病毒
披膜病毒 棒状病毒 正粘病毒
布尼奥罗病毒 冠状病毒
阿
雷
那
病
毒
反
转
病
毒
副
粘
病
毒
Uptake of animal virus occurs often by
endocytosis
?Endocytosis (内吞效应）
Consequences
of virus infection
in animal cells
Positive-Strand RNA Animal Viruses
?Picornavirus family:
– polioviruses
– cold viruses
– hepatitis A virus
– foot-and mouth viruses
+ Strand RNA
Animal Viruses
?The Poliovirus
Negative-Strand RNA Viruses
?Rhabdoviruses,rabies viruses
?Orthomyxoviruses,influenza virus
Influenza Viruses
Segmented genome
8 linear single-
stranded molecules
ranging in size from
890-2341 nucleotides
Antigenic shift:
piece of the RNA
genome from two
distinct strains
become associated.
Bacteriophages M13,f1 and fd
?Distinct Properties of M13
– Infect Escherichia coli
– Infect only male cells through attachment to
the male-specific pilus
– Have circular single-stranded DNA
– Can be used as a cloning vector and DNA
sequencing vehicle in genetic engineering
– Infect but not kill the cells
M13 leaves an infected cell without lysis
Double-Stranded DNA Bacteriophage,the first
discovered phage and the most extensively
studied ds DNA viruses,Example,T7
1,Linear double-stranded DNA with 39,936 base pairs
2,92% DNA codes for protein
3,Gene overlap through translation in different reading
frame and through internal translational
reinitiation as well as internal frame shifts.
4,One of the coded proteins inhibits the host restriction
system,it is synthesized before the entire T7
genome enters the cells.
Genetic
Map of T7
Early transcription occurs
when left end enters cells
A host RNA polymerase
is used just to copy the
first few genes and to
make the mRNA that
codes for the phage-
specific RNA polymerase
Two other early mRNA
code for proteins which
stop the action of host
RNA polymerase
DNA Replication in T7
In both direction,an
RNA primer is involved.
Rightward,RNA primer
is synthesized by T7
RNA polymerase
Leftward,RNA primer is
synthesized by
T7 primase
Both primers are elongated
by T7 DNA polymerase.
DNA Replication in T7
DNA Replication
in T7
?T7 has a much
more complex
replication
scheme than
that seen for the
other bacterial
viruses.
Large Double-Stranded DNA bacteriophages,
the T-even Phages T2,T4 and T6
?T4 (as example)
– 1.7 X 105 base pairs
– Have a unique base,5-hydroxymethylcytosine
instead of cytosine
– The above hydroxyl group is modified by
addition of glucosyl residues
– This glucosylated DNA is resistant to virtually
all restriction endonucleases of the host
DNA replication in T4
Time course of events in phage T4 infection
DNA Replication
in T4
? The cutting enzyme
which forms virus-
sized fragments does
not recognize specific
locations on the long
molecule,but cuts off
DNA irrespective of
the sequence.
? Thus,each virus DNA
sequences at the end of
different molecules are
different.
Temperate Bacterial Viruses,
Lysogeny and Lambda
?Virulent Viruses
?Temperate Viruses
– Lysogeny (溶原性）,Viruses can enter a state
called lysogeny,where most phage genes are
not expressed,and the phage genome is
replicated in synchrony with the host
chromosome
– Prophage or provirus
– Can be induced (lysogenic induction) by UV
radiation,nitrogen mustards or X-ray.
Temperate Bacterial
Viruses,
Lysogeny and
Lambda
Temperate Phage,Lambda
?Linear double-stranded DNA
?Single-stranded tail of 12 nucleotides long
at the 5’-terminus
?These single-stranded ends are
complementary (cohesive)
?The two ends can associate and form a
double-stranded circle containing 48,502
base pairs.
Electron Micrograph of
Lambda particles
Genetic and
Molecular Map
of Lambda
PR,Lytic cycle
PL,Lysogeny
Lytic Growth
of Lambda
?DNA
damage is
caused by
UV,X-ray,
Chemicals
etc.
The
Integration
of lambda
DNA into
the host
chromosome
Lambda Phage
Lambda DNA replication,Circular form (initially)
and Rolling Circle replication (late stage)
Bacterial
Viruses
Main types of
bacterial
viruses.
Sizes are
approximat
e scale
Transposable Phage,Bacteriophage Mu
?Mu,a mutator phage,which has the unusual
property of replicating as a movable genetic
element (a piece of DNA acts as
transposable element)
?Can be used to generate a wide variety of
bacterial mutants very easily
? Three types of transposable elements,
insertion elements,transposons and viruses
like Mu
Transposable Phage,Bacteriophage Mu
?Large double-stranded DNA virus
?39 KB DNA
?Only 37.2 KB is the actual Mu genome,the
rest is host DNA (50-150 base pairs at the left,
1-2 KB at the right end)
?The head of Mu can be filled with foreign
DNA and it brings the foreign genes to other
host cells (transduction)
?Contribute to genetic variation
Bacteriophage
Mu
?Genetic
map of Mu
?Integration
of Mu into
the host
DNA.
Animal Viruses (DNA Viruses)
DNA Viruses
Parvovirus (细小病毒 )
Papovavirus (乳头多
瘤空泡病毒）
Adenovirus （腺病毒）
Iridovirus (虹彩病毒 )
Hepadnavirus (肝炎
DNA病毒）
Poxvirus (天花病毒）
Herpesvirus (疱疹病
毒）
Animal Viruses (RNA Viruses)
小 RNA病毒
呼吸道肠道病毒
披膜病毒 棒状病毒 正粘病毒
布尼奥罗病毒 冠状病毒
阿
雷
那
病
毒
反
转
病
毒
副
粘
病
毒
Uptake of animal virus occurs often by
endocytosis
?Endocytosis (内吞效应）
Consequences
of virus infection
in animal cells
Positive-Strand RNA Animal Viruses
?Picornavirus family:
– polioviruses
– cold viruses
– hepatitis A virus
– foot-and mouth viruses
+ Strand RNA
Animal Viruses
?The Poliovirus
Negative-Strand RNA Viruses
?Rhabdoviruses,rabies viruses
?Orthomyxoviruses,influenza virus
Influenza Viruses
Segmented genome
8 linear single-
stranded molecules
ranging in size from
890-2341 nucleotides
Antigenic shift:
piece of the RNA
genome from two
distinct strains
become associated.
