draw a replica of the yeast plate with a circular nitrocellulose or nylon filter
dry the filter for a few minutes
briefly put the filter with tweezers into liquid nitrogen to break the cells
prepare the petri dish with a Whatman filter, then add 3 ml of Z-Buffer plus 150 ul of X-Gal solution ( 20 mg/ml dissolved in DMF)
place the replica filter onto top of the wet Whatman filter
Incubate at 30ĄC until blue staining develops (from 1 to 24 hours)

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