No abstract

No abstract

The minimal salts medium contained 2 g of NH4Cl, 6 g of Na2HPO4, 3 g of KH2PO4, 3 g of NaCl, and 0.25 g of MgSO4 in 1 liter of distilled water. Sodium succinate, glyceroL and glucose at 0.1% and sodium acetate at 0.2% were used as a carbon source. Various amino acids at 50 jAg/ml and Casamino Acids at 0.2% final concentration were added as indicated. 559 on August 28, 2020 by guest http://jb.asm.org/ Downloaded from ' 3 aa, Spplemted with amino acids methionone, histdine, arginine. A 6 aa, Spplemented with the three amino acids in footnote fplus proline, threonine, and tryptophan. 12 aa, Supplemented with the six amino acids in footnote g plus senne, leucine, tyrosine, alanine, asparagine, and aspartic acid.

When cultures of Escherichia coli B/r growing at various rates were exposed to ultraviolet light, mitomycin C, or nalidixic acid, deoxyribonucleic acid (DNA) synthesis stopped but cell division continued for at least 20 min. The chromosome configurations in the cells which divided were estimated by determining the rate of DNA synthesis during the division cycle. The cultures were pulse-labeled with 14Cthymidine, and the amount of label incorporated into cells of different ages was found by measuring the radioactivity in cells born subsequent to the labeling period. The cells which divided in the absence of DNA synthesis were those which had completed a round of chromosome replication prior to the treatments. It was concluded that completion of a round of replication is a necessary and sufficient condition of DNA synthesis for cell division.

ml) was added. The methanol-chloroform mixture was placed in new vials, each containing a 24-mm filter disk, and evaporated to dryness at room temperature, and the radioactivity on the filters was counted. The incorporation of radioactivity in the methanol-chlo-453 on July 31, 2020 by guest