Download BACTERIAL VIRUSES ("Bacteriophage") “Mein Gott!” They`ve got

BACTERIAL VIRUSES ("Bacteriophage")
READING: BOM-10
Chapter 9
Chapter 9
Chapter 9
Chapter 9
Chapter 9
Chapter 9
Chapter 16
Section I.
Section II.
Section III.
Section 9.8
Section 9.9
Section 9.10
Section 16.1
VIRUS AND VIRION
GROWTH AND QUANTIFICATION
VIRAL AND REPLICATION
Overview of Bacterial Viruses
Virulent Bacteriophage:T4
Temperate Bacteriophage:Lambda
RNA Bacvteriophages
p.232
p.232
p.240
p.246
p.247
p.250
p. 521
“Mein Gott!” They’ve got tails!”
J.J. Bronfenbrenner, on being shown the first electron
micrographs of phage in 1942.
1.
What essential features of cells do viruses lack?
2.
What is lysogeny and what is the essential difference between the lysogenic
state for M13 the lsoygenic state for the bacterial virus Lambda?
3.
What types of cell surface structures may serve as receptors for bacterial
viruses?
4.
What is the distinction between resistance and immunity to phage infection?
5.
RNA bacteriophage genomes have a gene for a novel type of enzyme not
ordinarily found in cells. Describe the activit/ function this type of enzyme.
6.
A single copy of the A protein of RNA bacterio[page R17 is present in the virion
capsid. Describe the 2 functions of this protein.
REASONS FOR STUDYING BACTERIOPHAGES
Classic model systems in molecular Biology
Cloning Vectors (Lambda, M13)
Ecology (Virioplankton)
Phage Therapy
Study of host parasite co-evolution.
VOCABULARY
Bacteriophage
a virus that infects and replicates ina bacterial host cell; some
times shortened to “phage”. Synonomous wit “bacterial virus”. The
term “coliphage” is sometimes used to designate bacteriophage
that infect and replicate in E. coli host cells.
Capsid
the protein surrounding the nucleic acid genome of a virion
Virion
the virus as it exists outside its host cell. Virions of most phage
consist of a nucleic acid genome surrounded by a protein capsid.
Lysogen
a bacterium that carries a temperate phage genome
Prophage
the genome of a temperate phage while in a lysogen.
Lysogeny
the process whereby a temperate phage establishes a relationship
with a host cell to create a lysogen..
Immunity
immunity is a property of a lysogen, conferred on it by expression of
one or more genes of its resident prophage, that renders it immune
to infection by other viruses related to the prophage .
Resistance
an inherited property of a bacterium that renders it unsusceptible to
infection by a phage. Resistance is usually due to lack of the
appropriate molecular receptor on the surface of the bacterium.
Lytic Infection
an infection which leads directly to viral replication and killing of
host cell.
Virulent Phage
a phage that is incapable of lysogeny
Temperate Phage
a phage that is capable of either lytic or lysogenic cycle.
Small RNA Plus-Strand RNA Bacteriophages
Examples:
Qβ, MS2, R17, f2, fr
The small RNA bacteriophages have several interesting properties.
•
They have the smallest genomes of any known virus, coding for only 3 or 4 gene
products.
•
DNA is not part of the life cycle. The basic molecular processes of DNA replication
and transcription are not involved.
•
These virus have a unique enzymatic activity, an RNA-dependent RNA polymerase,
not ordinarily found in any cellular organism. This type of enzyme would have been
required in an RNA WORLD.
The main difference between the example in the book "MS2", and the example in the
diagram below, is the presence of a discrete (overlapping) gene for a lysis protein in
MS2. In R17 the lysis function is incorporated in a domain of the maturation protein.
A (Maturation) 330 amino acids
1 copy per virion
host recognition (pilus)
host cell lysis (inhibits MurA, first step of peptidoglycan synthesis)
Coat Protein
Replicase
129 aa
180 copies per virion
580 aa
an RNA-dependent RNA Polynmerase
assembles with 3 E. coli ribosomal proteins
Tu: translational elongation factor; 393 aa binds aatRNA's GTPase
Ts: translational elongation factor; 282 aa GDP/GTP exchange on
Tu
S1: 557aa 30S ribosomal subunit
Qβ replicase has been used in some intriguing experiments in in vitro evolution and in a
biotecnological application referred to as SELEX technology. SELEX is an application of
the in vitro RNA replication to a "evolve a drug" strategy. http://www.lmb.unimuenchen.de/groups/famulok/SELEX.html
The 3 gene products of the R17 genome are needed in wildly different amounts;
(coat/Maturation 180/1). and, there being no transcruption involved, regulation is at
translational level. The ribosome binding site for tranlation of the A (maturation) protein
is obscured by + strand secondary structure which only becomes accessible as the
replicase unwinds the region. Replicase gene expression must not be done this way.
Coat protein binds to ribsosome binding site #3 an reduces translation.