Reverse transcriptase-related (RVT) proteins are a distinct class of domesticated reverse transcriptases (RTs) with unusual properties. This is the only RT type found in bacteria, fungi, protists, plants and invertebrates from aquatic and soil-dwelling environments. RVTs are encoded by cellular single-copy non-mobile genes preserved by natural selection, potentially performing biological function that is applicable to both prokaryotes and eukaryotes. Domestication of RT domain that makes DNA using RNA templates is extremely rare in eukaryotes, although it was described several times in prokaryotes. Our group aims to reveal cellular function(s) of RVT proteins.
We focused on three free-living organisms often dwelling in activated sludge with active rvt genes in their genome (the filamentous gliding bacterium Herpetosiphon aurantiacus, the model ascomycete fungus Neurospora crassa, and the bdelloid rotifer Adineta vaga). Free-living organisms can be frequently exposed to hazardous pollutants including transition metals, antibiotics and other chemicals that disrupt protein synthesis. Therefore, those organisms need potent mechanisms to cope with such stresses. We show that the examined organisms display signs of altered growth and behavior after exposure to increased concentrations of several metal ions (Ni2+, Co2+, Fe2+, Zn2+) or antibiotics (eg. Blasticidin S) in growth media and are characterized by strongly induced expression of rvt genes.
To discover the cellular function of RVT proteins, we applied various comparative genomic, transcriptomic, biochemical, structural, and functional approaches, as well as bioinformatic analyses of genomic and environmental datasets. Comparing results obtained for chosen bacterial, fungal and animal models, we conclude that RVT is involved in response to diverse environmental stresses via template-independent polymerization. Furthermore, when recombinant RVT from H. aurantiacus was expressed in E. coli, bacterial clones demonstrated a notable improvement in survival on iron-rich medium. This ability to work in a heterologous system can make RVT proteins a useful tool for biotechnological applications.