Dipartimento di Chimica Organica e Biologica, Università di Napoli, Italy.
A DNA fragment containing the trpEGC gene cluster was isolated from the thermoacidophilic archaebacterium Sulfolobus solfataricus. The products of trpE, trpG, and trpC from S. solfataricus were compared to the homologous products from a eukaryote, a eubacterium, and two archaebacteria, namely, a methanogen and an extreme halophile. They appeared to be equally related to the proteins from Escherichia coli and Saccharomyces cerevisiae, the percentages of conserved amino acids being roughly the same as those measured when comparing the eubacterial and eukaryotic sequences directly. These percentages did not rise significantly when a comparison with the proteins from Haloferax volcanii was drawn, while a slightly closer relationship with the proteins from Methanococcus thermoautotrophicum was found.