文档介绍：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 ic 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.
ic 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 plex 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)
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 do