Rickettsia prowazekii, the causative agent of epidemic typhus, has been responsible for millions of human deaths. Madrid E is an attenuated strain of R. prowazekii, while Breinl is a virulent strain. The genomic DNA sequence of Madrid E has recently been published. To study the genomic variations between Madrid E (reference) and Breinl (test) DNAs, cohybridization experiments were performed on a DNA microarray containing all 834 protein-coding genes of Madrid E. Of the 834 genes assessed, 24 genes showed 1.5-to 2.0-fold increases in hybridization signals in Breinl DNA compared to Madrid E DNA, indicating the presence of genomic variations in ϳ3% of the total genes. Eighteen of these 24 genes are predicted to be involved in different functions. Southern blot analysis of five genes, virB4, ftsK, rfbE, lpxA, and rpoH, suggested the presence of an additional paralog(s) in Breinl, which might be related to the observed increase in hybridization signals. Studies by real-time reverse transcription-PCR revealed an increase in expression of

We previously reported that the presence of the bacterial (Vitreoscilla) hemoglobin gene enhances alpha-amylase production in recombinant Escherichia coli strain MK79. Using the growth of MK79 on starch as a selective method we have produced a mutant strain (BSC9) that produces up to four times as much alpha-amylase as MK79. Both MK79 and BSC9 produce the most alpha-amylase (per cell and per milliliter) in the stationary phase; almost all of the enzyme is intracellular in both strains. Modification of the standard alpha-amylase assay increases the amount of amylase detected about sixfold. BSC9 has about five to nine times as many copies per cell as MK79 of the recombinant plasmid, which carries both the amylase and hemoglobin genes, but both strains produce about the same amount of hemoglobin. While MK79 respiration decreases upon going from log to stationary phase, BSC9 respiration increases during the same period. The two latter results may be of particular importance in determining the way in which hemoglobin enhances the production of cloned protein products in recombinant bacteria.

Relatively little work has been done on the influence of the position of the cell in the cell cycle on ionizing radiation-induced mutagenesis. We synchronized WTK1 human lymphoblastoid cells with 200 microM lovastatin for 48 h; under these conditions more than 80% of the cells were arrested in G1 phase. Upon release, there was a 12-15-h lag followed by movement of a large fraction into S phase. We irradiated cells with either 1.5 Gy X rays at 1, 15, 18, 21 or 24 h or 1.5 Gy gamma rays at 1, 5, 10, 15 or 24 h after release from lovastatin. We showed that WTK1 cells were most sensitive to ionizing radiation-induced toxicity in G1 and into S phase, and more resistant in mid to late S and G2/M phase. Somewhat surprisingly, we found that the two different gene loci had different sensitivities to radiation-induced mutation through the cell cycle. Cells in late G1 through mid-S phase were most sensitive to radiation-induced mutations at the autosomal thymidine kinase (TK) locus, whereas G1 phase was the most sensitive phase at the X-linked hypoxanthine guanine phosphoribosyl transferase (HPRT) locus.

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