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Ancestral Sequence Reconstruction$
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David A Liberles

Print publication date: 2007

Print ISBN-13: 9780199299188

Published to Oxford Scholarship Online: September 2008

DOI: 10.1093/acprof:oso/9780199299188.001.0001

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A thermophilic last universal ancestor inferred from its estimated amino acid composition

A thermophilic last universal ancestor inferred from its estimated amino acid composition

Chapter:
(p.200) CHAPTER 17 A thermophilic last universal ancestor inferred from its estimated amino acid composition
Source:
Ancestral Sequence Reconstruction
Author(s):

Dawn J. Brooks

Eric A. Gaucher

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780199299188.003.0017

The last universal ancestor (LUA) represents a relatively accessible theoretical intermediary between extant cellular organisms and early, precellular ‘life’. In a previous study, the expectation-maximization (EM) approach was used to infer ancestral amino acid frequencies, where in each iteration expected counts were derived from posterior distributions at each site. Applying this approach to estimate the amino acid composition of 65 proteins in the LUA showed that composition was more similar to that of extant thermophiles than mesophiles. This chapter examines whether the previous result is robust with respect to the OGT of the taxa used to infer the amino acid composition of proteins in the LUA. It is shown that even if only mesophilic species are used to derive the estimated ancestral amino acid composition, that composition is most similar to that of thermophiles, as measured by Euclidean distance. The relative mean Euclidean distance between the amino acid composition in any one species and that of a set of mesophiles or thermophiles can be used unequivocally to classify it. Thus, the inferred amino acid composition in the LUA allows its classification as a thermophile.

Keywords:   last universal ancestor, amino acids, thermophile, mesophile

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