Discovery of bacterial genes encoding isocytosine deaminases

Abstract

Modified nucleotides are present in almost all classes of RNA. They have great chemical diversity and are critical for RNA folding, stability, interaction with cellular proteins and thereby for various cellular processes such as translation, stress response, and signaling pathways. Biosynthesis of pyrimidine nucleotides and their modified derivatives in RNA is well studied. Nonetheless, not much is known about the cellular degradation of these compounds and the enzymes catalyzing such processes. Using an E. coli uracil auxotrophic strain, we screened metagenomic libraries for genes encoding isocytosine deaminases. Three novel genes were obtained, one of which encodes a protein similar to 8- oxoguanine deaminases. The other two encode proteins resembling hydroxydechloroatrazine ethylaminohydrolases. We confirmed that these proteins are functional in vivo, allowing growth of E.coli on minimal medium with isocytosine. We also demonstrated that such purified recombinant enzymes catalyze the conversion of isocytosine, but not cytosine, into uracil in vitro. This work is supported by the Research Council of Lithuania (LMT, SEN-07/2015).