PFGE was performed as previously described63 (link),73 (link). Briefly agarose plugs have been run in a 1% agarose gel (Bio-Rad PFGE agarose) prepared in 150 ml of TBE 0.5× and the migration chamber was filled with 3 litres of TBE 0.5×. The Amersham Gene Navigator System was used with a water refrigerating bath set at 4 °C. The gel was run at 165 V for 24 h with 30 s pulses (step wise) for the separation of the chromosomes XII.
For the isolation of the rDNA array genomic DNA embedded in the plugs was digested with BamHI74 (link) and digested plugs were run into the PFGE as described above using the following run conditions :100 V for 69 h (step 1 = 68 h with pulses of 300 s and step 2 = 1 h with 900 s pulses; the two steps were connected by the interpolation mode). During the PFGE run pulses went from 300 to 900 s.
For the isolation of the rDNA array genomic DNA embedded in the plugs was digested with BamHI74 (link) and digested plugs were run into the PFGE as described above using the following run conditions :100 V for 69 h (step 1 = 68 h with pulses of 300 s and step 2 = 1 h with 900 s pulses; the two steps were connected by the interpolation mode). During the PFGE run pulses went from 300 to 900 s.
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