Effects of HIV-1 viral proteins on colony formation. Wild type S. pombe cells containing HIV-1 viral gene-expressing plasmids were grown overnight in EMM liquid medium supplemented with thiamine to mid-log phase. The following day, cells were recovered, re-suspended in fresh media and streaked onto the minimal selection EMM agar plates with thiamine (left +T plates; no gene expression) or without thiamine (right −T plates; with gene expression). The plates were incubated at 30°C for 6 days before observation. The pYZ1N-vpr and pYZ1N plasmids were used as positive and negative controls, respectively .