BASE ANALOGUE INDUCED ARABINOSE-NEGATIVE MUTANTS OF ESCHERICHIA COLI.

Abstract

EOXYRIBONUCLEIC acid codes information as a specific linear sequence of the base pairs adenine-thymine (AT) and guanine-cytosine (GC) ( WATSON and CRICK 1953). Replacement of an AT pair by a GC pair, o r a GC pair by an AT pais may cause a visible mutation. A transition is a base-pair change as written above in which a purine replaces a purine, and a pyrimidine replaces a pyrimidine (FREESE 1963). Consideration of possible hydrogen-bonding led FREESE ( 1959) to suggest that 2-aminopurine (AP) should cause both AT to GC and GC to AT transitions. The chemical specificity of hydroxylamine (HA) for cytosine and the revertibility of HA-induced mutants by AP suggest that HA causes only GC to AT transitions ( FREESE, BAUTZ-FREESE and BAUTZ 1961a). Those mutants which are AT to GC changes should show increased reversion rates back to wild type under the influence of HA, while GC to AT changes should not revert under the influence of HA. These two classes of AP induced mutants, found for the bacterial virus T4 (FREESE et al., 1961a,b) will be described for bacteria. 5-bromodeoxyuridine (BUDR) should cause AT to GC and GC to AT transitions, depending on whether the transition occurs during incorporation of the BUDR into DNA, or during replication of BUDR labeled DNA (FREESE 1963). Evidence supporting this hypothesis has been obtained from bacterial viruses ( FREESE 1963; TERZAGHI, STREISINGER and STAHL 1962) and bacteria (RUDNER 1961; STRELZOFF 1961, 1962), although in uitro experiments indicate that BUDR causes nontransition as well as transition DNA changes ( TRAUTNER, SWARTZ, and KORNBERG 1962). We will give evidence for the existence of BUDR induced transition and nontransition bacterial mutants. For discussions of specific mutagens see FREESE ( 1963), CLOWES (1964), and HAYES (1964).