Protein phylogenies: A reappraisal of the evolutionary relationships between archaebacteria, eubacteria and eukaryotes
Gupta, R.S.
McMaster University, Hamilton L8N 3Z5, Canada
Global phylogenies and signature sequences in different proteins show that the primary division within prokaryotes is between Monoderm prokaryotes (surrounded by a single membrane) and Diderm prokaryotes (containing both an inner cytoplasmic membrane and an outer membrane). Both archaebacteria and Gram-positive bacteria are monoderm prokaryotes, a relationship strongly supported by cell morphology and signature sequences in different proteins. The monophyletic nature of archaebacteria as suggested by genes primarily related to information transfer, and their polyphyletic branching within Gram-positive bacteria as suggested by others, is critically examined and several explanations, including derivation of archaebacteria from Gram-positive bacteria in response to antibiotic selection pressure, are proposed. The diderm prokaryotes (i.e., Gram-negative bacteria), which are indicated to be derived from monoderm prokaryotes, form a structurally and phylogenetically distinct clade. The protein phylogenies and signature sequences also provide evidence that all eukaryotic cells received major gene contributions from both an archaebacterium (monoderm) and a Gram-negative eubacterium (diderm). The ancestal eukaryotic cell, thus, rather than being a direct descendent of an archaebacteria, is a chimera that resulted from a unique fusion event between these groups of prokaryotes. The possibility that all eubacterial contribution to the nuclear genome may be due to endosymbiotic (mitochondrial) gene replacement is inconsistent with the phylogenies and signature sequences in well studied genes. Thus the current three domain classification which posits that the primary division within prokaryotes is between archaebacteria and eubacteria and that archaebacteria and eukaryote shared a common ancestor exclusive of eubacteria is untenable.
| LOCATION |
DATE |
TIME |
| Lecture Hall I |
Sunday, April 5 |
02:00 pm |