Reverse transcriptase-related (rvt ) genes represent a remarkable class of reverse transcriptases (RTs) found in bacteria, fungi, protists, plants and invertebrates from aquatic and soil-dwelling environments. These are cellular single-copy genes preserved by natural selection. Their occurrence in prokaryotic and eukaryotic representatives suggests a conserved biological function that is applicable to both prokaryotes and eukaryotes.
RVT proteins from the filamentous gliding bacterium Herpetosiphon aurantiacus and the ascomycete fungus Neurospora crassa display a peculiar property of initiating polymerization via protein priming. Thus, RVTs represent the first known case of protein-primed RT encoded by a chromosomal non-selfish gene. Moreover, the N-terminal coiled-coil domain allows RVT proteins to form multimers and could potentially interact with metal ions. Since most free-living organisms can be frequently exposed to hazardous pollutants including transition metals, they therefore need potent mechanisms to cope with such stresses.
Three free-living organisms with active rvt genes in their genome (H. aurantiacus , N. crassa and the bdelloid rotifer Adineta vaga,) not only display signs of altered growth and behavior after treatment with varying concentrations of several metal ions (Ni2+, Co2+, Fe2+ etc.) but also display strongly induced expression of rvt genes under metal stress conditions. Interestingly, all examined organisms demonstrate specificity of rvt response to a specific metal ion. Moreover, when recombinant bacterial HaRVT is expressed in E. coli, it apparently provides an advantage for survival in iron-rich environments. Participation of domesticated RTs in metal stress response could reveal an ancient function of these genes in early evolution and novel pathways to environmental adaptation.