Biomedical subjects

D A Rowe-Magnus

Publications and source records attributed to D A Rowe-Magnus.

8 recordsLinked to original sources

PubMed2001

The evolutionary history of chromosomal super-integrons provides an ancestry for multiresistant integrons.

Integrons are genetic elements that acquire and exchange exogenous DNA, known as gene cassettes, by a site-specific recombination mechanism. Characterized gene cassettes consist of a target recombination sequence (attC site) usually associated with a single open reading frame coding for an antibiotic resistance determinant. The affiliation of multiresistant integrons (MRIs), which contain various combinations of antibiotic resistance gene cassettes, with transferable elements underlies the rapid evolution of multidrug resistance among diverse Gram-negative bacteria. Yet the origin of MRIs remains unknown. Recently, a chromosomal super-integron (SI) harboring hundreds of cassettes was identified in the Vibrio cholerae genome. Here, we demonstrate that the activity of its associated integrase is identical to that of the MRI integrase, IntI1. We have also identified equivalent integron superstructures in nine distinct genera throughout the gamma-proteobacterial radiation. Phylogenetic analysis revealed that the evolutionary history of the system paralleled that of the radiation, indicating that integrons are ancient structures. The attC sites of the 63 antibiotic-resistance gene cassettes identified thus far in MRIs are highly variable. Strikingly, one-fifth of these were virtually identical to the highly related yet species-specific attC sites of the SIs described here. Furthermore, antimicrobial resistance homologues were identified among the thousands of genes entrapped by these SIs. Because the gene cassettes of SIs are substrates for MRIs, these data identify SIs as the source of contemporary MRIs and their cassettes. However, our demonstration of the metabolic functions, beyond antibiotic resistance and virulence, of three distinct SI gene cassettes indicates that integrons function as a general gene-capture system for bacterial innovation.

Alteromonas↗

PubMed2001

Integrons: natural tools for bacterial genome evolution.

Integrons were first identified as the primary mechanism for antibiotic resistance gene capture and dissemination among Gram-negative bacteria. More recently, their role in genome evolution has been extended with the discovery of larger integron structures, the super-integrons, as genuine components of the genomes of many species throughout the gamma-proteobacterial radiation. The functional platforms of these integrons appear to be sedentary, whereas their gene cassette contents are highly variable. Nevertheless, the gene cassettes for which an activity has been experimentally demonstrated encode proteins related to simple adaptive functions and their recruitment is seen as providing the bacterial host with a selective advantage. The widespread occurrence of the integron system among Gram-negative bacteria is discussed, with special focus on the super-integrons. Some of the adaptive functions encoded by these genes are also reviewed, and implications of integron-mediated genome evolution in the emergence of novel bacterial species are highlighted.

DNA Transposable Elements↗

PubMed2000

Identification of a second region of the Spo0A response regulator of Bacillus subtilis required for transcription activation.

Deletion of the 10 C-terminal amino acids of the Bacillus subtilis response regulator Spo0A or valine substitution at D258 and L260 resulted in a sporulation-negative phenotype and loss of in vivo activation of the spoIIG and spoIIA operon promoters. Repression of the abrB promoter was not affected by the mutations. In combination with the previously characterized mutation (A257V), the results identify amino acids at positions 257, 258, and 260 as being required for transcription activation by Spo0A.

Amino Acid Sequence↗

PubMed1999

Resistance gene capture.

Integrons are the primary mechanism for antibiotic-resistance gene capture and dissemination among Gram-negative bacteria. The recent finding of super-integron structures in the genomes of several bacterial species has expanded their role in genome evolution and suggests that they are the source of mobile multi-resistant integrons.

Anti-Bacterial Agents↗

PubMed1998

Contributions of the domains of the Bacillus subtilis response regulator Spo0A to transcription stimulation of the spoIIG operon.

Spo0A is a response regulator that controls entry into sporulation by specifically stimulating or repressing transcription of critical developmental genes. Response regulators have at least two domains: an output transcription regulation domain and a receiver domain that inhibits the output domain. Phosphorylation of the receiver domain relieves the inhibition. We examined the in vitro transcription activation mechanism for Spo0A, phosphorylated Spo0A (Spo0A approximately P), and a deletion mutant that consists solely of the C-terminal output domain (Spo0ABD). Both Spo0A approximately P and Spo0ABD stimulated transcription from the spoIIG promoter 10-fold more efficiently than Spo0A. Spo0A approximately P and Spo0ABD induced DNA denaturation by RNA polymerase in the -10 recognition region, whereas Spo0A did not. DNase I footprint assays revealed that phosphorylation enhanced binding of intact Spo0A to the 0A boxes, while the binding of Spo0ABD was similar to that of Spo0A. Thus, activation of Spo0A by phosphorylation is not primarily due to enhanced DNA binding. The presence of a phosphorylated N terminus increased the stability of the ternary complex at the spoIIG promoter. We propose that the primary effect of phosphorylation is to expose an RNA polymerase interaction domain to promote transcription from PspoIIG.

Bacillus subtilis↗

PubMed1998

DNA strand separation during activation of a developmental promoter by the Bacillus subtilis response regulator Spo0A.

Spo0A is the central regulator of commitment to sporulation in Bacillus subtilis. Spo0A is a member of the response regulator family of proteins and both represses and stimulates transcription from promoters when activated. In vivo Spo0A activation takes place by phosphorylation and in vitro activation can be accomplished by phosphorylation or removal of the N-terminal domain of the protein. We have examined the mechanism of Spo0A stimulation of transcription from the promoter of the spoIIG operon. This operon encodes one of the first compartment specific sigma factors whose appearance regulates sporulation development. When activated Spo0A was incubated with RNA polymerase and a DNA fragment containing the spoIIG promoter, bases between -13 and -3, relative to the start site of transcription, were denatured. Addition of activated Spo0A or RNA polymerase alone did not induce denaturation. Heteroduplex templates that contained the nontemplate sequence of the wild-type promoter on both strands between positions -3 and -13 were efficiently transcribed without activated Spo0A. These data suggest that DNA strand separation is a two-step process and that the activation of Spo0A creates a form that interacts with the polymerase to induce the first of the two steps.

Bacillus subtilis↗

PubMed1998

Transcriptional activation of the Bacillus subtilis spoIIG promoter by the response regulator Spo0A is independent of the C-terminal domain of the RNA polymerase alpha subunit.

In vitro transcription from the spoIIG promoter by Bacillus subtilis RNA polymerase reconstituted with wild-type alpha subunits and with C-terminal deletion mutants of the alpha subunit was equally stimulated by the response regulator Spo0A. Some differences in the structure of open complexes formed by RNA polymerase containing alpha subunit mutants were noted, although the wild-type and mutant polymerases appeared to use the same initiation mechanism.

Bacillus subtilis↗

PubMedDate not supplied

Super-integrons.

Integrons represent the primary mechanism for antibiotic resistance gene capture and dissemination among gram-negative bacteria. The recent finding of super-integron (SI) structures in the genomes of several bacterial species has expanded their role in genome evolution. The Vibrio cholerae superintegron is gathered in a single chromosomal super-structure harbouring hundreds of gene cassettes. The encoded functions, when identifiable, are linked to adaptations extending beyond antibiotic resistance and pathogenicity. Comparison of the cassette contents of super-integrons from remote Vibrio species suggests that most of their cassettes are species-specific. Many bacterial species belonging to several distinct genera of the gamma- and beta-proteobacteria undoubtedly carry or show strong evidence for the presence of chromosomal SIs. If each bacterial species harbouring a SI has its own cassette pool, the resource in terms of gene cassette availability may be immense.

Base Sequence↗