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Tobacco mosaic virus

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Tobacco mosaic virus
M.M. Hernandez
Tobacco mosaic virus
• Genus Tobamovirus
15 members
naked, rigid rod,
+ unsegmented ss RNA
• No family assignation by ICTV
30 nm
Helical symmetry
RNA genome
18 nm
2 nm
NC protein
Images:P. Sforza, 2001
TMV genome organization
6,395 nt
Capsid CP
Replicase RdRp
5’ cap
126 K
17.6 K
30 K
UAG (leaky)
Movement MP
Host: Nicotiana tabaccum
(Solanaceous ) & other 9 plant families
susceptible too
Disease:Mosaic (calico)
Mosaic disease on Tobacco leaf
Mosaic disease: significant losses in yield & $ value
TMV Life cycle
5’ cap
Host Rb
a) Virus entry trough
abrasions on plant
tissue. Inside cell
associates with ER
b) spontaneous release
of few capsid (CP)
subunits 5' end of
genome is uncovered
c) Host ribosome
attaches to viral RNA,
moves down displacing
more CP units …/…
Modification of a diagram from: L. Stannard, Department of Medical Microbiology, U. of Cape Town
TMV Life cycle
d) Ribosome meets start
codon, translates first two
proteins (126K ,183 K) while
uncoating continues
“co-traslational disassembly”
e) 126 K ( MET-Hel) & 183 K
( RdRp) use viral RNA as
template to make full length
complementary neg. strand
Modification of a diagram from: L. Stannard, Department of Medical Microbiology, U. of Cape Town
TMV Life cycle
+ Strand (genome)
Neg. strand
f) Neg. RNA strand used
by viral replicase
(RdPp/MET-Hel ) as
template for +RNA
g) Also, neg. RNA strand
has internal promoters
used by replicase to
make mRNA for 30K
protein (MP) and 17.5 K
Transcription by RdRp
TMV Life cycle
h) MP combines
with viral +RNA
to move it into
new plant cells
TMV Life cycle
i) Accumulation of +RNA
& CP proteins stimulates
assembly of progeny
Viral RNA interacts with
CP units self assemble
into discs
Electrostatic interaction stabilizes structure
into helix
M. Olvera de la Cruz
TMV Life cycle
j) massive TMR replication
occur in the X-bodies
Szecsi et al. 1999
Hamacher et al. 2003
TMV Life cycle
k) Virus will remain in plant tissue and sap until delivered to
a new plant host usually by mechanical means
TMV diagnosis
• Symptoms
• E.M. & Serology
Letschert et al. 2002
Current Research on TMV
• Improving diagnostic
• Characterization of
MP and viral
movement through
• Characterization of
the Helicase & RdRp
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1. Solution of TMV Capsid Proteins
Electrostatic repulsion inhibits
2. Add ssTMV+ RNA (assembly
infective virus): Electrostatic
attraction stabilizes viral assembly.
+ protein +protein aggregation.
Salt (M)
ZRNA= -1/mer
3. Sphere-like (icosahedral) RNA virus
(Tsuruta et al)
4. Capsid + Hole (density ≈ RNA crystal)
self-assembles from capsid protein + viral
RNA solution
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