The hycD gene product is part of the formate hydrogenlyase complex; the tnaL gene encodes tryptophanase; the cryptic bglB gene encodes phospho-beta-glucosidase; b1011 is required for utilization of pyrimidines; b0941 encodes a fimbrin subunit; b2209 encodes a serine protease inhibitor; the spoT gene product is a ppGpp pyrophosphohydrolase; and sgcC encodes a predicted phosphotransferase. There was no overlap between wildtype and the recA strains in genes showing increased Cyclosporine expression after BLM treatment in glucose minimal medium. Genes showing greater than a two-fold decrease in transcription were few and not informative. The microarray analysis did not, therefore, reveal a transcriptional mechanism responsible for BLM resistance. It should be noted that the array data represent only a single set of mRNA samples. For E. coli cells D-Pantothenic acid sodium growing in broth, exposure to BLM results in the formation of DSBs. We base this conclusion on the detection of such breaks by pulse field gel electrophoresis; by the induction of the SOS regulon; and by the requirement for homologous recombination for cells to survive BLM challenge. The requirement for the RecBCD pathway of homologous recombination, and not the RecF pathway, is consistent with the preferential ability of this pathway to repair DSBs. Single-strand breaks are also formed based on the sensitivity of DNA ligase mutant strains. These results for cells growing in broth were expected based on previous studies with other cytotoxic agents. While this work was in progress, Nichols et al. published the results of a high throughput method to determine E. coli phenotypes using the response of the Keio collection strains to various drugs including BLM. These studies were conducted in cells growing in rich media. In general, the results of their study are in agreement with those reported here in terms of the requirement for recombination gene products and DNA ligase. In addition, the Nichols et al. study identified hfq, fis, rusA and sbcA mutant strains as BLM sensitive as well as a large number of mutant bacteria affecting the structure/function of the cell envelope. The RusA and SbcA proteins are part of a prophage recombination system. The requirement for Hfq likely reflects a requirement for one or more small regulatory non-coding RNA molecules and their study identified istR and gvcB although additional RNA molecules are possible. The Fis protein is important to maintain nucleoid integrity. In sum, both studies indicate the importance of recombination in the resistance of E. coli cells growing in broth to BLM. The results of the Nichols et al. study also confirmed the data from two previous investigations. Girgis et al. mutagenized E. coli with a transposon and selected for mutant strains with greater or less resistance to a panel of antibiotics including BLM. Becket et al. screened the Keio collection for sensitivity to various antibiotics. These determinations were carried out in L broth and, in general, the results from all three studies are in agreement.