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The IrrE Protein of Deinococcus radiodurans R1 Is a Novel Regulator of recA Expression. Ashlee M. Earl, 2002.IRS24 is a DNA damage-sensitive strain of Deinococcus radiodurans strain 302 carrying a mutation in an uncharacterized locus designated irrE . Five overlapping cosmids capable of restoring ionizing radiation resistance to IRS24 were isolated from a genomic library . The ends of each cloned insert were sequenced, and these sequences were used to localize irrE to a 970-bp region on chromosome I of D . radiodurans R1 . The irrE gene corresponds to coding sequence DR0167 in the R1 genome . The irrE gene encodes a 35,000-Da protein that has no similarity to any previously characterized peptide . The irrE locus of R1 was also inactivated by transposon mutagenesis, and this strain was sensitive to ionizing radiation, UV light, and mitomycin C . Preliminary findings indicate that IrrE is a novel regulatory protein that stimulates transcription of the recA gene following exposure to ionizing radiation . Lack of the ApbC or ApbE Protein Results in a Defect in Fe-S Cluster Metabolism in Salmonella enterica Serovar Typhimurium. Elizabeth Skovran, 2003.The isc genes function in the assembly of Fe-S clusters and are conserved in many prokaryotic and eukaryotic organisms . In most bacteria studied, the isc operon can be deleted without loss of cell viability, indicating that additional systems for Fe-S cluster assembly must exist . Several laboratories have described nutritional and biochemical defects resulting from mutations in the isc operon . Here we demonstrate that null mutations in two genes of unknown function, apbC and apbE, result in similar cellular deficiencies . Exogenous ferric chloride suppressed these deficiencies in the apbC and apbE mutants, distinguishing them from previously described isc mutants . The deficiencies caused by the apbC and isc mutations were additive, which is consistent with Isc and ApbC's having redundant functions or with Isc and ApbC's functioning in different areas of Fe-S cluster metabolism (e.g., Fe-S cluster assembly and Fe-S cluster repair) . Both the ApbC and ApbE proteins are similar in sequence to proteins that function in metal cofactor assembly . Like the enzymes with sequence similarity to ApbC, purified ApbC protein was able to hydrolyze ATP . The data herein are consistent with the hypothesis that the ApbC and ApbE proteins function in Fe-S cluster metabolism in vivo . Starvation Survival Response of Mycobacterium tuberculosis. Tanya Parish, 2003.The ability of Mycobacterium tuberculosis auxotrophs to survive long-term starvation was measured . Tryptophan and histidine auxotrophs did not survive single-amino-acid starvation, whereas a proline auxotroph did . All three auxotrophs survived complete starvation . THP-1 cells were also able to restrict the growth of the tryptophan and histidine auxotrophs . –1 Frameshifting at a CGA AAG Hexanucleotide Site Is Required for Transposition of Insertion Sequence IS1222. Nina Mejlhede, 2004.The discovery of programmed –1 frameshifting at the hexanucleotide shift site CGA_AAG, in addition to the classical X_XXY_YYZ heptanucleotide shift sequences, prompted a search for instances among eubacterial insertion sequence elements . IS1222 has a CGA_AAG shift site . A genetic analysis revealed that frameshifting at this site is required for transposition . Characterization of the 4-Hydroxybenzoyl-Coenzyme A Thioesterase from Arthrobacter sp . Strain SU. Zhihao Zhuang, 2003.The Arthrobacter sp . strain SU 4-chlorobenzoate (4-CBA) dehalogenation pathway converts 4-CBA to 4-hydroxybenzoate (4-HBA) . The pathway operon contains the genes fcbA, fcbB, and fcbC (A . Schmitz, K . H . Gartemann, J . Fiedler, E . Grund, and R . Eichenlaub, Appl . Environ . Microbiol . 58:4068-4071, 1992) . Genes fcbA and fcbB encode 4-CBA-coenzyme A (CoA) ligase and 4-CBA-CoA dehalogenase, respectively, whereas the function of fcbC is not known . We subcloned fcbC and expressed it in Escherichia coli, and we purified and characterized the FcbC protein . A substrate activity screen identified benzoyl-CoA thioesters as the most active substrates . Catalysis of 4-HBA-CoA hydrolysis to 4-HBA and CoA occurred with a kcat of 6.7 s-1 and a Km of 1.2 µM . The kcat pH rate profile for 4-HBA-CoA hydrolysis indicated optimal activity over a pH range of 6 to 10 . The amino acid sequence of the FcbC protein was compared to other sequences contained in the protein sequence data banks . A large number of sequence homologues of unknown function were identified . On the other hand, the 4-HBA-CoA thioesterases isolated from 4-CBA-degrading Pseudomonas strains did not share significant sequence identity with the FcbC protein, indicating early divergence of the thioesterase-encoding genes .
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