ANCIENT DIVERSITY OF THE GLUCOSE-6-PHOSPHATE ISOMERASE GENES

The DNA and deduced amino acid sequences of the glycolytic enzyme gluc ose-6-phosphate isomerase (PGI) were analyzed to infer the phyolgeneti c relationships among the PGI genes from eukaryotes and prokaryotes. T he inferred phylogeny of the PGI genes is at variance with the convent ional phylogenetic scheme of the organisms and suggests that (1) the P GI genes had separated into several lineages prior to the divergence o f eukaryotes and prokaryotes; and (2) the progenitor of present-day eu karyotes and prokaryotes already contained several divergent PGI genes . The relevance of the results to horizontal transfer of genes is disc ussed.