ALTERATION IN THE CONTENTS OF UNSATURATED FATTY-ACIDS IN DNAA MUTANTSOF ESCHERICHIA-COLI

DnaA protein, the initiator of chromosomal DNA replication in Escheric hia coli, has a high affinity for acidic phospholipids containing unsa turated fatty acids. We have examined here the fatty acid composition of phospholipids in dnaA mutants. A temperature-sensitive dnaA46 mutan t showed a lower lever of unsaturation of fatty acids (ratio of unsatu rated to saturated fatty acids) at 42 degrees C (non-permissive temper ature) and at 37 degrees C (semi-permissive temperature), but not at 2 8 degrees C (permissive temperature), compared with the wild-type stra in. Plasmid complementation analysis revealed that the dnaA46 mutation is responsible for the phenotype. Other temperature-sensitive dnaA mu tants showed similar results. On the other hand, a cold-sensitive dnaA cos mutant, in which over-initiation of DNA replication occurs at row temperature (28 degrees C), showed a higher level of unsaturation of f atty acids at 28 degrees C. Based on these observations, we discuss th e role of phospholipids in the regulation of the activity of DnaA prot ein.