Reverse Transcriptase Activity as a Marker for Virus-Like Particle Production

Begin with wells containing adherent mammalian cells co-transfected with plasmids encoding viral proteins and either a non-inhibitory control RNA or an inhibitory RNA.

In the control wells, viral proteins, including reverse transcriptase (RT), assemble into mature virus-like particles (VLPs) and are released into the supernatant.

In the test wells, the inhibitory RNA suppresses viral protein expression, reducing VLP production.

Transfer the supernatant to a lysis buffer and incubate to lyse the VLPs, releasing RT.

Add a buffer containing radiolabeled nucleotides, primers, a synthetic RNA template, and cofactors, then incubate.

The RT incorporates the labeled nucleotides into new strands.

Spot the mixture onto a charged filter paper, dry it, and wash with a buffer to remove unbound nucleotides.

Perform an alcohol wash to remove residual salts.

Measure radioactivity to quantify RT activity, indicating VLP production.

Reduced VLP production in test samples indicates suppression by the inhibitory RNA.

To carry out the viral production assay, after removing the 24-well cell culture plates from the incubator, transfer them to the BSL-3 cell culture hood. Gently swirl the plates and then transfer 150 microliters of the supernatant from each well to a corresponding well in a 96-well flat-bottom plate to be used to quantify HIV-1 production. Transfer 5 microliters of supernatant to the corresponding wells in a 96-well plate containing 25 microliters of a viral disruption cocktail.

After incubating the mixture for five minutes at room temperature, transfer the plate to a radioactivity work station. Next, prepare a radioactive cocktail, and add 25 microliters to each well of viral supernatant and disruption cocktail. Incubate the plates at 37 degrees Celsius for two hours.

Spot 5 microliters of the reaction mixture onto corresponding squares in a glass fiber DEAE filter mat paper, and allow the spots to dry for 10 minutes. Use 2x SSC buffer to wash the papers five times for five minutes each, followed by two one-minute washes with 95% ethanol. Allow the papers to dry before sealing them in sample bags.

Clip sample bags containing the filter mat paper into a cassette, and insert the cassette into a microplate scintillation counter. Then start the counter. For any viral quantification method, divide the values obtained for each test RNA by the adjacent negative control and multiply this value by 100 to get the percent inhibition of HIV-1 production for each replicate of the test RNAs.