Summary: The properties of a temperature-sensitive mutant (ts39) of 8235 are described. After transfer to the restrictive temperature (42 °C), absorbance increased 10-to 20-fold but DNA content did not increase beyond 150 to 200% and cell division continued at a greatly reduced rate. On transfer back to the permissive temperature, both cell division and DNA synthesis resumed if the transfer occurred after less than 120 min at 42 °C. Resumption of DNA replication was blocked by chloramphenicol (100 μg ml). The results are discussed with reference to possible defects in DNA replication.

Replication of the plasmids pI and pT and the chromosome were affected to a similar extent in ts39. Growth at 42 °C resulted in the appearance of an increased amount of pI DNA in a form that sedimented slowly in a sucrose gradient.


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