Characterization of two bacterial mutants with temperature-sensitive synthesis of DNA.

DESPITE considerable interest in recent years, the replication of bacterial DNA and the mechanism of its regulation are still poorly understood, as can be seen in recent reviews of the subject (LARK 1966; MAALBE and KJELDGAARD 1966). One approach to the study of essential cellular syntheses is through the study of temperature-sensitive mutants (APIRION 1966; EPSTEIN et al., 1963; NEIDHARDT 1966). Already several papers have appeared describing bacterial mutants impaired in synthesis of DNA at higher temperature ( BONHOEFFER 1966; KOHIYAMA et al. 1966; MENDELSON and GROSS 1967). The present report describes a procedure for the isolation of bacterial mutants with tcmperaturesensitive synthesis of DNA and the characterization of two mutants representative of the types which were most frequently encountered. The mutants studied resemble the two classes found previously (KOHIYAMA et al. 1966); but from the experiments presented here, it is evident that at least one of them represents a new kind of block in DNA synthesis. A preliminary report of these mutants has been presented ( FANGMAN 1966).