Ribonucleases H of retroviral and cellular origin

Ribonucleases H (RNases H) are enzymes which catalyse the hydrolysis of the RNA-strand of an RNA-DNA hybrid. Retroviral reverse transcriptases possess RNase H activity in addition to their RNA- as well as DNA-dependent DNA-polymerizing activity. These enzymes transcribe the viral single stranded RNA-genome into double stranded DNA, which then can be handled by the host cell like one of its own genes. Various, sometimes highly repeated, sequences related to retroviruses and like these encompassing two separate domains, one of which potentially codes for a DNA polymerizing, the other for an RNase H activity, are found in genomes of uninfected cells. In addition proteins coded for by cellular genes (e.g. from E. coli and from yeast) are known, which exhibit RNase H activity, the biological function of which is not fully understood. In the light of these facts the question of whether retroviral RNases H could be promising targets for antiviral drugs is discussed.