Evidence for the involvement of unsaturated fatty acids in initiating chromosome replication in Escherichia coli

The analogue 3-decynoyl-N-acetylcysteamine inhibits the synthesis of unsaturated fatty acids in Escherichia coli, resulting in the accumulation of saturated fatty acids in the membrane (Kass, 1968).In the presence of this analogue, DNA, RNA and protein synthesis continue at a linear rate for approximately two doubling times, and then cease. On the other hand, the analogue will inhibit the formation of new replication forks (premature initiation), which normally arise as a result of thymine starvation.Unlike other temperature-sensitive DNA mutants, mutants that are defective in initiating DNA replication (dnaA or dnaC) are unable to replicate DNA at a permissive temperature if they terminate replication at 42 °C in the presence of 3-decynoyl-N-acetylcysteamine.When replication is terminated at 42 °C, cultures of dnaA or dnaC mutants normally will reinitiate replication upon lowering the temperature to 30 °C. For each mutant this reinitiation is characterized by a particular temperature sensitivity. Such mutants become more temperature sensitive if the temperature is lowered in the presence of 3-decynoyl-N-acetylcysteamine. All the effects of this analogue can be reversed by the addition of unsaturated fatty acids.These results are interpreted using a model in which replication is initiated at a particular lipid site on the membrane. In the absence of unsaturated fatty acids functional lipid sites are not made. Functional sites, however, can be used again provided they are not inactivated by interaction with an inactive dnaA or dnaC product.