400 ci 1 mmole to 3000 ci 1 mmole. The nick translation reaction was set up as recommended by the manufacturer of the kit, using about 0.5 ug DNA. The reaction was incubated at 12 -14 °C for 90 minutes, except in the case of small fragments ( 500 bp ) when the reaction was incubated for 45 minutes only. The reaction was terminated by the addition of stop buffer supplied with the kit.

DNA was labelled using the nick translation kits supplied by BRL or NEN, USA, or Amersham, UK. The 32P-deTP was from either NEN or Amersham, UK, at a concentration of 10 mei I ml. The specific activity of the label ranged from