PG AND RESEARCH DEPARTMENT OF MICROBIOLOGY, SRI PARAMAKALYANI COLLEGE, ALWARKURUCHI-627 412

1. Sri paramakalyani college
Alwarkurichi 627 412
COURSE TITLE: virology
COURSE WORK TITLE: MU phage
Submitted to,
GUIDE: Dr.C.MARIAPPAN, Ph.D,
ASSISTANT PROFESSOR,
SRI PARAMAKALYANI COLLEGE,
ALWARKURICHI.
Submitted by
Student name : S. Azhagammal
Register number : 20211232526107
Class : I M. Sc Microbiology
Date of Submission :

2. Synopsis
Mu phage
Structrue of mu phage
Genetic map of mu phage
The functions of different genes are as follows
Life Cycle of Mu Phage
Reference

3. MU phage
◦Phage Mu is also known as bacteriophage Mu.
◦Since it infects the members of enterobacteria, it is
also called enterobacteria phage Mu.
◦It belongs to the family Myoviridae and dsDNA
viruses.
◦Mu phage is alsocalled temperate or transposable
phage because it causes transposition of the genes
into the host cell, at the time of multiplication.

4. ◦Bacteriophage Mu, also known as mu
phage or mu bacteriophage, is a muvirus (the
first of its kind to be identified) of the
family Myoviridae which has been shown to cause
genetic transposition.
◦It is of particular importance as its discovery
in Escherichia coli by Larry Taylor was among
the first observations of insertion elements in a
genome.

6. Structure of Mu Phage
◦As we know the basic structure of the bacteriophage,
that is comprised of head, neck and tail.
◦The structure of Mu phage is also divided into three
parts i.e. head neck and tail
◦Head : It is the terminal part of the Mu phage which
carries the viral genome and surrounds by a protein
layer refers as Capsid.
◦The head of Mu phage is having icosahedral
symmetry.

7. ◦The shape is like spheroid.
◦The diameter is 54 nm.
◦Capsid is the layer which surrounds the hexagonal
head.
◦The capsid of Mu phage is composed of about 152
smaller protein subunits, known as “Capsomeres”
◦Neck: It is the middle portion of the Mu phage, acts
as the joining element which joins the two
components i.e. Head and tail.

8. ◦Tail : It is long, thick and contractile because of the
presence of cross bands.
◦The size of the tail is 183 X 16-20nm.
◦Sheath is the covering of the contractile tail, which
is composed of stacked rings.
◦At the time of contraction, the sheath becomes
shorter and thicker.
◦And the length of the sheath during contraction is up
to 60-90nm.
◦Tails fibers are thin and thread-like structures which
are attached to the large base plate.
◦There are six long terminal fibres.

9. Genetic map of Mu Phage
◦Mu phage consists of a ds-DNA which is linear,
◦The genome of Mu phage consists of 37,611 base
pairs.
◦The guanine and cytosine content is 35%.
◦Genome consists of some unusual base
pairs(hydroxy methyl uracil) and terminally
redundant sequences.
◦Mu phage genome encodes 55 genes which perform
different functions in its life cycle.

10. ◦

11. The functions of different genes are as
follows:
◦Mu-phage consists of two transposase binding sites that
bind to the host DNA and represented as attL and attR.
These two ends sometimes called as MuL and MuR.
◦A gene: It encodes all transposition events.
◦B gene: It encodes the all replicative transposition.
◦C gene: It represses the expression of the transposase gene.
◦Head and tail genes: These are the structural genes that
help in reconstruction or biosynthesis of Mu phage.
◦Gin gene: It catalyzes the site-specific inversion reactions.

12. ◦Mom gene: It encodes a DNA modification function by
converting adenine to acetamide adenine.
◦Lye gene: It encodes the lytic enzyme, which causes lysis
of the host cell.

13. Life Cycle of Mu Phage
Its lifecycle can be summarized in the following steps:
Attachment : Firstly, the tail fibres attach to the receptor site of
the host cell surface. By the binding of the tail fibre, there is the
conformational change in the base plate of Mu phage. Due to the
conformational change in the base plate, the tail’s sheath contracts.
Penetration : By the contraction of the tail’s sheath, the rigid
internal material gets into the host cell surface through the cell
envelope. The N protein ( non-replicative protein) also gets injected
along with the viral genome.

15. Circularization:The N-protein undergoes circularization
once it binds with the viral genome.
Integration: After circularization, early transcription
occurs that gives rise to the Repc and Ner repressors and
DDE recombinase A (Mu A). These genes help in the
integration of the viral genome with the host genome.
During this step, the variable ends are cut off from the
viral genome.

16. Early phase: After the non-replicative transposition, the
ratio of Repc and Ner repressors decide whether the phage
will enter to the lysogenic phage or lytic phage.
◦Repc: It represses the early promoter by establishing
latency or lysogeny.
◦Ner: It represses the expression of Repc by promoting the
expression of the early genes for the replication of Mu
phage.

17. Middle phase
After the inactivation of Repc, there is an
expression of MuA and MuB genes. MuA is the DDE
recombinase-A enzyme, and MuB is the target DNA
activator B. MuA performs the transposition of viral
genome ends and host DNA. The target DNA activator B
helps in the replication of viral host DNA, leading to the
formation of the two copies. This type of replication is
called replicative transposition. This replication can lead
to 100 viral genomes after successive rounds.

18. Late transcription
This phase carries out the expression of the
adenine modification enzyme, which makes the viral
DNA resistant to the host restriction enzymes by
modifying the adenines in the viral DNA.

19. Biosynthesis and Assembly : The late gene synthesizes the
structural genes of Mu phage, which leads to the biosynthesis
of virus particles. Then the virus particles like empty capsid,
tail fibres etc. get to assemble.
The packaging of virion: Firstly, the bacterial DNA is first
cut on the left of the integrated Mu genome for about 50-
150bp. Then, a second cut occurs after the filling of phage
head. The packaging of viral DNA also occurs on the right
side of the Mu genome. Therefore, at different sites of the
bacterial genome, the packaging of the Mu genome will occur.

20. Cell lysis and release of virion
After packaging, the newly synthesized virions
release out of the host cell by the help of lye gene that
encodes lytic enzymes (responsible for the cell lysis).

21. Reference
◦Morgan, GJ; et al. (2002), "Bacteriophage Mu genome
sequence: analysis and comparison with Mu-like
prophages in Haemophilus, Neisseria and Deinococcus", J
Mol Biol, 317 (3): 337–
359, doi:10.1006/jmbi.2002.5437, PMID 11922669
◦Montano SP, Pigli YZ, Rice PA (2012).
◦https://biologyreader.com/mu-phage.html.