Nonpermissive Condition (Molecular Biology)

The condition under which a conditional lethal mutant cannot grow is called the nonpermissive or restrictive condition. In contrast, the permissive condition allows growth. Typical nonpermissive conditions are high or low temperature, extremes of pH, osmotic pressure, oxygen concentration, and the absence of growth factors. Particular hosts can become nonpermissive or restrictive for mutant strains of viruses, bacteriophages, or other parasites (see Conditional Lethal Mutations).