The universal ancestor was a thermophile or a hyperthermophile.
By exploiting the correlation between the optimal growth temperature of organisms and a thermophily index based on the propensity of amino acids to enter thermophile/hyperthermophile proteins, an analysis is conducted in order to establish whether the last universal common ancestor (LUCA) was a mesophile or a (hyper)thermophile. This objective is reached by using maximum parsimony and maximum likelihood to reconstruct the ancestral sequences of the LUCA for two pairs of sets of paralogous protein sequences by means of the phylogenetic tree topology derived from the small subunit ribosomal RNA, even if this is rooted in all three possible ways. The thermophily index of all the reconstructed ancestral sequences of the LUCA belongs to the set of the thermophile/hyperthermophile sequences, thus supporting the hypotheses that see the LUCA as a thermophile or a hyperthermophile.
Di Giulio
M
M
International Institute of Genetics and Biophysics, CNR, Via G. Marconi 10, 80125 Naples, Italy. digiulio@iigb.na.cnr.it
D000064:Acclimatization / Q000235:genetics*; D000595:Amino Acid Sequence; D002455:Cell Division / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D018271:Signal Recognition Particle / Q000235:genetics; D013696:Temperature; D014369:Tryptophan-tRNA Ligase / Q000235:genetics
C069268:SRP54 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle; D014369:Tryptophan-tRNA Ligase