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•TITLE PAGE: Is protein sequence evolution constant over time? MIEP08 12 June 2008 Carolin Kosiol & Nick Goldman http:/

acid sequences

likelihood substitution

substitution matrices

protein sequences

markov behaviour

amino acid

constant over time

Voir

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Nombre de lectures

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6 Mo

•TITLE PAGE:
Is protein sequence evolution
constant over time?
Carolin Kosiol &
Nick Goldman
goldman@ebi.ac.uk
http:/www.ebi.ac.uk/goldman
MIEP08
12 June 2008Are Markov process models appropriateconvert to question about Markov
for protein sequence evolution?
processesEvidence of non-Markov evolution
of amino acid sequencesevidence of non-Markov behaviour
Amino Acid Substitution Matrices From Protein Blocks
S. Henikoff and J.G. Henikoff
Proceedings of the National Academy of Sciences
of the United States of America 89:10915–10919. 1992
Tree-based Maximal Likelihood Substitution Matrices
and Hidden Markov Models
G. Mitchison and R. Durbin
Journal of Molecular Evolution 41:1139–1151. 1995
Amino Acid Substitution During Functionally
Constrained Divergent Evolution of Protein Sequences
S.A. Benner, M.A. Cohen and G.H. Gonnet
Protein Engineering 7:1323–1332. 1994P(t) = exp(tQ) etc …
instantaneous
rate matrix
time
probability of change
(as a function of time)Q … and in pictures= = =
t
∞time t0
≠ ≠ ≠P(t)It is possible
to infer P(t)
We can estimate P(t) from data …
from sequence data……and possible
to infer Q
We can estimate Q from P(t) …from P(t)
A
R
N WAG
D
C
Q
E
G
H
I
L
K
M
F
P
S
T
W
Y
V
A R N D C Q E G H I L K M F P S T W Y V… and in pictures
time t
“Matrix space”not constant, according to
Henikoff x 2 (BLOSUM)
… and in picturesand Mitchison & Durbin
time t
“Matrix space”Benner et al. evidence
Benner et al. found rate matrix elements
varied with observed divergence
They argued that the genetic code
influences the matrix strongly at early stages
of divergence, while physicochemical
properties are dominant at later stages