HI I am working on porcine tissue and looking for porcine endogenous retrovirus and testing its infectivity on HEK cell line by RT activity assay. It has been suggested that we should check the RT activity using the supernatant in an interval of 3 days for 24 days. I would like to know whether i can store the supernatant collected every 3 days and altogether do the RT activity assay? or I should do the assay soon after I collected the supernatant?