Figure 7.

Southern blotting. (a) 10 μg DNA from the injection site of five PCR-positive fish (fish a–e), and one control fish (CMV-0 injected muscle), were digested with Kpn I and Xba I restiction endonucleases to release a 3·2-kb lacZ fragment which was detected by a fluorescein-labelled lacZ probe in fish c, d and e. (b) Undigested DNA from differing tissues was detected by a fluorescein-labelled probe for lacZ. The injected muscle, but no other tissue, shows the three forms of plasmid DNA: linear, closed and open circles. The three samples of gut each contained a different lacZ band with a molecular weight which was distinct from that of any other sample. (c) 10 μg DNA from differing tissues was cleaved with Hin dIII and detected by the probe to the plasmid backbone. The fragment was only in the muscle and was of the same length as pCMV-lacZ.