Antonio Tormo

The ftsA gene product: a possible connection between DNA replication and septation in Escherichia coli.

The study of Escherichia coli strain D-2, which harbours the ftsA2(ts) allele, has shown that temperature-induced filaments of this strain can divide, at 30 degrees C, in the absence of DNA replication and translation. Strain D-2 is thermosensitive during a period coincident with that in which the termination protein should be synthesized and exert its action. The ftsA gene product, which participates in the structure of the septum, needs for its synthesis a short period of DNA replication. The FtsA protein could be involved in a mechanism that coordinates chromosome replication and cell division by a pathway different from and independent of the SOS-induced response.

Co-ordination between elongation and division in Escherichia coli mediated by the wee gene product.

A procedure to construct strains of Escherichia coli containing conditional lethal mutations in two different genes was used to construct a ftsA-3(ts) wee(Am) supF(ts) strain. This strain, OV-25-7, was used to ascertain whether the wee gene product (Wee) acts at the level of regulation of cell elongation or at the co-ordination of elongation and division. The mass per unit length and the buoyant density of cells in the absence of Wee increased only if division was allowed, as in the case of strain OV-25 (wee(Am) supF(ts)), but not when it was inhibited, as in strain OV-25-7. These results suggested that in E. coli the wee gene product was acting at the level of coordination between elongation and cell division.

Segregation of elongation potential inEscherichia coli mediated by thewee genetic system

Under normal conditions, the two cells within a pair ofEscherichia coli siblings elongate at a similar rate. Genetic impairment of thewee genetic system leads to significant variations in the rate of elongation of each cell within a given pair of siblings. This result is in accordance with previous reports that showed the need of active cell division for expression of the Wee phenotype. The genetic location of one element of the system,weeA, has been determined to be at min 67 of theE. coli map; this does not coincide with the previously reported genetic location. The inability to reproduce the Wee phenotype in a wild-type background by transduction ofweeA suggests that more genetic elements should participate in the segregation of elongation zones at cell division.