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#Post#: 70--------------------------------------------------
Coronaviruses
By: gsgs Date: February 7, 2020, 9:21 pm
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“There is some evidence that people can be reinfected with the
four coronaviruses
and that there is no long-lasting immunity,”
SARS has a molecular proofreading system that reduces its
mutation rate, and the
new coronavirus’s similarity to SARS at the genomic level
suggests it does, too.
“That makes the mutation rate much, much lower than for flu or
HIV,” Farzan said.
HTML https://www.statnews.com/2020/02/04/two-scenarios-if-new-coronavirus-isnt-contained/
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Thus nsp14-ExoN is essential for replication fidelity, and
likely serves either as a direct
mediator or regulator of a more complex RNA proofreading
machine, a process previously
unprecedented in RNA virus biology. E
The discovery of a protein distinct from a viral RdRp that
regulates replication fidelity also
raises the possibility that RNA genome replication fidelity may
be adaptable to differing
replication environments and selective pressures, rather than
being a fixed determinant.
Proofreading Exoribonuclease.
Coronaviruses genome also encodes a protein called a replicase
which allows
the RNA viral genome to be transcribed into new RNA copies
using the host cell's machinery.
The replicase is the first protein to be made; once the gene
encoding the replicase
is translated, translation is stopped by a stop codon.
This is known as a nested transcript. When the mRNA transcript
only encodes
one gene, it is monocistronic.
A coronavirus non-structural protein provides extra fidelity to
replication because it
confers a proofreading function,[9] which is lacking in
RNA-dependent RNA
polymerase enzymes alone.
Sexton NR, Smith EC, Blanc H, Vignuzzi M, Peersen OB, Denison MR
(August 2016).
"Homology-Based Identification of a Mutation in the Coronavirus
RNA-Dependent RNA
Polymerase That Confers Resistance to Multiple Mutagens".
Journal of Virology. 90 (16): 7415–7428.
doi:10.1128/JVI.00080-16. PMC 4984655. PMID 27279608.
CoVs encode a proofreading exonuclease in nonstructural protein
14(nsp14-ExoN),
which confers a greater-than-10
fold increase in fidelity compared to other RNA viruses. It is
unknown to what extent the CoV
polymerase (nsp12-RdRp) participates in replication fidelity
multiproteinreplicase-proofreadingcomplex.
Proofreading-deficient coronaviruses adapt for increased fitness
over long-term passage
without reversion of exoribonuclease-inactivating mutations
Alanine replacement of the motif I residues (AA-E-D; four
nucleotide substitutions) in
murine hepatitis virus (MHV) and severe acute respiratory
syndrome (SARS)-CoV yields
viable mutants with impaired replication and fitness, increased
mutation rates, and attenuated
virulence in vivo. Despite these impairments, MHV- and SARS-CoV
ExoN motif I AA mutants
(ExoN-AA) have not reverted at motif I in diverse in vitro and
in vivo environments, suggesting
that profound fitness barriers prevent motif I reversion
The Amazing Diversity of Nidoviruses
#Post#: 268--------------------------------------------------
Re: Coronaviruses
By: gsgs Date: December 26, 2020, 11:52 pm
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human non-sars-like Coronaviruses at genbank , release 239.0 :
1394, Human coronavirus OC43
907, Human coronavirus NL63
424, Human coronavirus 229E
415, Human coronavirus HKU1
195, unidentified human coronavirus
6, Human enteric coronavirus 4408
4, Human coronavirus Feline-like Hu142
2, Human betacoronavirus 2c Jordan-N3/2012
2, Human betacoronavirus 2c EMC/2012
1, Human group 1 coronavirus associated with pneumonia
1, Human enteric coronavirus strain 4408
1, Human coronavirus type 5
1, Human coronavirus NO/2708/04
1, Human coronavirus NO/1917/04
1, Human coronavirus NO/1055/04
1, Human coronavirus NO/0867/04
1, Human coronavirus NO/0848/04
1, Human coronavirus NO/0835/04
1, Human coronavirus NO/0749/04
1, Human coronavirus NO/0733/05
1, Human coronavirus NO/0643/05
1, Human coronavirus NO/0398/05
1, Human coronavirus NO/0341/04
1, Human coronavirus NO/0193/05
1, Human coronavirus NO/0053/04
1, Human coronavirus NO/0023/05
1, Human coronavirus NO/0003/05
1, Human coronavirus 3363/2000/NL
1, Human coronavirus 1196/2001/NL
1, Human betacoronavirus 2c England-Qatar/2012
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