Genetic and physical maps of Klebsiella aerogenes genes for histidine utilization ( hut )

Deletion derivatives of the hut -containing plasmid pCB101 were tested against point mutants defective in individual genes of the histidine utilization ( hut ) operons using a complementation/recombination assay. Location of the genes of the right operon, hutU and hutH , was confirmed by direct assay of the gene products, urocanase and histidase; location of the repressor gene was identified by measuring the ability of the plasmid-carried genes to repress the formation of histidase from a chromosomal location. The analysis of eight deletion plasmids unambiguously confirms the map order of the hut genes as hutI-G-C-U-H , and demonstrates that, in Klebsiella aerogenes , the hutU and hutH genes are transcribed from their own promoter. In addition, the genetic map of hut can be aligned with the restriction map of the hut DNA in plasmid pCB101. One of the deletion plasmids studied apparently encodes a defective histidase subunit that is trans-dominant to active histidase. Another deletion, which completely removes the left operon, hutIG , allows high level expression of the hutUH operon and thus overproduction of a toxic intermediate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47553/1/438_2004_Article_BF00327421.pd

4-(4-nitrobenzyl)pyridine tests for alkylating agents following chemical oxidative activation

A chemical activation system (CAS) designed to mimic the mammalian mixed-function oxidase enzymes was found to activate target compounds to reactive electrophiles. Activated compounds were assayed by reaction with 4-(4-nitrobenzyl)pyridine (NBP). A model nucleophile of 7-alkylguanine of nucleic acids, NBP produces a violet color following alkylation. Twenty compounds from several chemical classes were tested. The test generally gave positive and negative responses where expected. Two compounds, trichloroethylene and diethylnitrosamine, exhibited a linear Beer's law relationship in the concentration range tested. A high degree of linear correlation (r>0.97) was obtained for these compounds. Other compounds showed varying degrees of linear correlation from high correlation (r=0.94) to weak correlation (r=0.44). The CAS-NBP assay results were compared to bacterial mutagenicity and animal carcinogenicity test results when information was available. A good correlation (r=0.80) existed between direct alkylating activity and direct mutagenicity. Similar correlations existed between NBP alkylation following activation and mutagenicity following microsomal activation (r=0.73). Also, different correlations were observed between carcinogenicity and NBP alkylation following activation (r=0.69) and without activation (r=0.38).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48076/1/244_2004_Article_BF00213289.pd

Isolation of glutamate-inserting ochre suppressor mutants of Salmonella typhimurium and Escherichia coli.

Glutamate-inserting ochre suppressors have been identified among late-arising, spontaneous revertants of a hisG428 mutant of Salmonella typhimurium and an argE3 mutant of Escherichia coli. The S. typhimurium suppressors mapped in the tRNA2(Glu) gene gltU at 82 min; those in E. coli were found to be in tRNA2(Glu) genes gltW at 56 min, gltU at 85 min, and gltT at 90 min