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  • 1995-1999  (2)
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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In a search for genes involved in regulation of the 2′-N-acetyltransferase in Providencia stuartii, a mini-Tn5 Cm insertion has been isolated in a locus designated aarD. The aarD1::mini-Tn5 Cm mutation resulted in a 4.7-fold increase in the levels of β-galactosidase accumulation from an aac(2′)–lacZ transcriptional fusion and a 32-fold increase in the levels of gentamicin resistance in P. stuartii. The wild-type aarD locus was cloned on a 5.0 kb Cla I fragment and complemented the aarD1 mutation. Nucleotide sequence analysis of this fragment identified two large open reading frames whose deduced products displayed significant amino acid identity, 64% and 64%, respectively, to the CydD and CydC proteins of Escherichia coli, which are involved in formation of the cytochrome d oxidase complex. Physical mapping indicated the aarD1::mini-Tn5 Cm insertion was within the open reading homologous to CydD. The strain containing the aarD1 mutation was unable to grow in the presence of toluidine blue or on glycerol minimal media in the presence of zinc, suggesting that aarD is functionally equivalent to cydD. Additional phenotypes resulting from the aarD1 mutation included: altered cell morphology, a reduced growth rate and the inability of cells to grow beyond early log phase. Further examination of this phenomenon revealed that the aarD1 mutant was unable to grow in the presence of a self-produced extracellular factor(s). This novel phenotype was not limited to P. stuartii as E. coli cydD and ΔcydAB::kan mutants were also sensitive to a self-produced extracellular factor.
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  • 2
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A recessive mutation, aarG1, has been identified that resulted in an 18-fold increase in the expression of β-galactosidase from an aac(2′)–lacZ fusion. Transcriptional fusions and Northern blot analysis demonstrated that the aarG1 allele also resulted in a large increase in the expression of aarP, a gene encoding a transcriptional activator of aac(2′)-Ia. The effects of aarG1 on aac(2′)-Ia expression were mediated by aarP-dependent and -independent mechanisms. The aarG1 allele also resulted in a multiple antibiotic resistance (Mar) phenotype, which included increased chloramphenicol, tetracycline and fluoroquinolone resistance. This Mar phenotype also resulted from aarP-dependent and -independent mechanisms. Sequence analysis of the aarG locus revealed the presence of two open reading frames, designated aarR and aarG, organized in tandem. The putative AarR protein displayed 75% amino acid identity to the response regulator PhoP, and the AarG protein displayed 57% amino acid identity to the sensor kinase PhoQ. The aarG1 mutation, a C to T substitution, resulted in a threonine to isoleucine substitution at position 279 (T279I) in the putative sensor kinase. The AarG product was functionally similar to PhoQ, as it was able to restore wild-type levels of maganin resistance to a Salmonella typhimurium phoQ mutant. However, expression of the aarP and aac(2′)-Ia genes was not significantly affected by the levels of Mg2+ or Ca2+, suggesting that aarG senses a signal other than divalent cations.
    Type of Medium: Electronic Resource
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