Mechanisms of genome evolution in Rickettsia
Hiroyuki OGATA
Information Génétique et Structurale,CNRS-AVENTIS UMR1889,
31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
Our recent comparative analysis of Rickettsia conorii (1.3 Mbp) and
R. prowazekii (1.1 Mbp) has revealed unexpected mechanisms of genome
evolution [1]. Both Rickettsia exhibited palindromic repeats
(100-150 bases) dispersed in their genome. Surprisingly, many of those
palindromic sequences were identified within predicted ORFs.
A systematic analysis reveals three different palindromic sequence
families (RPE-1, 2 and 3) exhibiting this phenomenon. We verified that
those repeats are indeed translated and retained as supplementary amino-acid
sequences in the final proteins, without affecting their fold and function [2].
Thus RPEs appear to represent a new class of selfish DNA encoding a
"selfish peptide". The comparison of the two genomes also evidenced a
very gradual nature of the genome reduction process. We identified different
intermediates from intact ORFs: a truncated protein, transcribed split
ORFs, transcriptionally inactive split ORFs, decayed but still
recognizable ORFs, and complete gene elimination.
The evolutionary significance of those phenomena will be discussed.
[1] Ogata et al.: Science, 290, 347-350, 2000; Science, 291, 252-253, 2001;
Science, 293, 2093-2098, 2001; 2002 (submitted).
[2] Monchois et al.: 2002 (submitted).
International Summer School - From Genome to Life:
Structural, Functional and Evolutionary approaches
(July 15-27, 2002, Corsica, France)