Divergence of Methanogens, Conservation of the His I Gene Sequence in all Three Biological Kingdoms and the Status of Methanobacterium Thermoautotrophicum

Methanogens are archaebacteria [1]. It was therefore somewhat surprising when it was shown that methanogen-derived genes could function in eubacterial species [2]. This has offered the opportunity of using gene cloning in Escherichia coli to investigate the basic structure of methanogen genes [3, 4] and to use E. coli to synthesize methanogen enzymes involved in methanogenesis [5] and nitrogen fixation [6].