Inhibition by RNA of RNase H activity associated with reverse transcriptase in Rauscher murine leukemia virus cores

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.

Simple affinity procedure for the purification of mammalian viral reverse transcriptases

Polyguanylic acid was found to be a potent inhibitor of RNase H associated with mammalian viral reverse transcriptase, indicating a strong interaction between polyguanylic acid and the reverse transcriptase protein. Based on this observation, we have developed three simple procedures for the purification of mammalian viral reverse transcriptases. In the first procedure, a nucleic acid-free extract of Rauscher murine leukemia virus was applied to a column of phosphocellulose and the reverse transcriptase was eluted by a low concentration (50 microM) of polyguanylic acid. Polyadenylic acid and polyuridylic acid could not replace polyguanylic acid for the elution. In the second procedure, a polyuridylic acid-Sepharose column was substituted for phosphocellulose, and the elution was again achieved by polyguanylic acid. In the third affinity procedure, the reverse transcriptase in a nucleic acid-free viral extract was incubated in the cold with 50 microM polyguanylic acid and the complex was adsorbed onto a DEAE-cellulose column. After washing to remove uncomplexed and weakly complexed proteins, the reverse transcriptase was eluted in a concentrated form at 0.3 M NaCl with a recovery of greater than 70%. by polyacrylamide gel analysis in the presence of sodium dodecyl sulfate, the enzyme appeared to be nearly pure.