 comparison mutat inactiv rate induc bacteriophag transform dna mutagen inactiv mutat rate measur t4 phage bacillu subtili transform dna treat low ph nitrou acid hydroxylamin temperatur frequenc mutant increas linearli time three agent logarithm surviv linear plot nitrou acid low ph arrheniu plot slope inactiv mutat rate treatment low ph nitrou acid agent slope remain unalt dna treat denatur contrast mutat rate exposur hydroxylamin differ greatli nativ denatur dna phage t4 intermedi treatment low ph nitrou acid interrupt genet linkag tryptophan histidin interrupt hit 1 3 frequent lethal hit independ temperatur 