Plasmid replication and the induced synthesis of colicins E1 and E2 in Escherichia coli.

Induction of colicins E1 and E2 in Escherichia coli occurs when plasmid synthesis has been inhibited either by nalidixic acid or by lack of deoxyribonucleic acid polymerase I. Moreover, colicin E1 and E2 synthesis induced by mitomycin C and exposure to chloramphenicol is not associated with a large increase in circular plasmid deoxyribonucleic acid. The mean plasmid content of cells in populations having a low spontaneous frequency of colicin-producing cells because of growth at low temperature or because of the presence of recA(-) or crp(-) alleles, is not significantly different to that in wild-type cells grown at 37 C.

The apparent absence of a pathway for synthesis of acetyl coenzyme A in pea chloroplasts: Lack of (14)CO 2 incorporation into lipids by the isolated organelle.

We have examined the extent to which isotopic lable derived from photosynthetically fixed (14)CO2 can be transferred to lipids by aqueously isolated chloroplasts of Pisum sativum. Although photosynthetically active, chloroplast preparations incubated with (14)CO2 showed little or no accumulation of label in lipids under any condition tested. Under identical conditions the chloroplasts were readily able to incorporate [(14)C]acetate into the lipid fraction; a fatty-acid synthesizing system was therefore operative in these chloroplasts.

Isolation of supercoiled colicinogenic factor E 1 DNA sensitive to ribonuclease and alkali.

The synthesis of the covalently-closed, circular DNA form of colicinogenic factor E(1) (ColE(1)) continues in Escherichia coli cells after the addition of chloramphenicol. A large portion of the purified supercoiled ColE(1) DNA molecules made in the presence of chloramphenicol are converted to the open circular DNA form after treatment with alkali (pH 13), RNase A, or RNase H. These treatments do not significantly affect the covalently-closed form of ColE(1) DNA isolated from normally growing E.