THE CHARACTERISTICS AND GENETIC MAP LOCATION OF A TEMPERATURE SENSITIVE DNA MUTANT OF E. COLI K12

[摘要] A temperature sensitive strain of E. coli K12 has been isolated in which residual DNA synthesis occurs at the 40°C restrictive temperature; syntheses of RNA, protein and DNA precursors are not directly affected. The mutation has been designated dna-325 and is located at 89 min on the E. coli map in the same region where the dnaC locus is found. dnaC mutants are considered to be defective in DNA initiation. Some of the data are consistent with the view that the dna-325 mutation is temperature sensitive in the process of DNA initiation rather than DNA chain elongation: (1) more than two cell divisions occur after a shift to 40°C; (2) upon a shift down to 30°C, cell division occurs again only after the DNA content of the cells has doubled; (3) 80% more DNA is made at 30°C in the presence of chloramphenicol after prior inhibition of DNA synthesis at 40°C. These three observations indicate that rounds of DNA replication were completed at 40°C. Also (4) infective λ particles can be made at 40°C long after bacterial DNA replication has ceased. It appears however that some DNA initiation can occur at 40°C since (1) a limited amount of DNA synthesis does occur at 40°C after prior alignment of the chromosomes by amino acid starvation at 30°C, and (2) after incubation in bromouracil at the restrictive temperature, heavy DNA is found with both strands containing bromouracil.

[学科分类] 医学（综合）