ARE EUKARYOTIC AND PROKARYOTIC SIGNAL-TRANSDUCTION SYSTEMS EVOLUTIONARILY RELATED

Fundamental similarities have appeared in the structural and functional organization of signal-transducing systems which govern the action of hormones, hormone-like substances, and pheromones in a number of vertebrates and invertebrates (including single-celled organisms). Prokaryotes also possess functional mechanisms and molecular components of hormonal signalling similar to those in higher eukaryotes. On the basis of these similarities, it is hypothesized that signal-transducing systems originated in prokaryotes. This proposal is examined in the context of contemporary theories of the origin of the eukaryotic cell, its organelles and components. A hypothesis of endosymbiotic genesis of eukaryotic signal-transducing systems is proposed.