Yeast cells were grown at 30ºC, with orbital shaking at 300 rpm, in standard YNB
glucose medium supplemented with 20 mg/l L-tryptophan, 40 mg/l adenine and 20 mg/l
L-histidine. A standard lithium acetate protocol was used for production of competent
yeast and transformation (Burke et al., 2000). Transformants of the W303-1B strain
7
(carrying pEMBLyex or pEMBLyex-vpr plasmids) were maintained in selective
medium (containing 20 mg/l L-leucine). For vpr expression, yeast cells were cultured in
YNB medium containing 2% galactose plus required supplements (inducing medium).
The pH of media was adjusted with Trizma base. When required, solid medium was
prepared by the addition of 1.5 % purified agar (Difco) to the broth.