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M M Gibson

Publications and source records attributed to M M Gibson.

5 recordsLinked to original sources
PubMed1991

Peptide transport and chemotaxis in Escherichia coli and Salmonella typhimurium: characterization of the dipeptide permease (Dpp) and the dipeptide-binding protein.

The dipeptide permease (Dpp) is one of three genetically distinct peptide-transport systems in enteric bacteria. Dpp also plays a role in chemotaxis towards peptides. We have devised three selections for dpp mutations based on resistance to toxic peptides (bacilysin, valine-containing peptides, and bialaphos). All dpp mutations mapped to a single chromosomal locus between 77 and 78 min in Salmonella typhimurium and at 79.2 min in Escherichia coli. Expression of dpp was constitutive in both species but the absolute level of expression varied widely between strains. At least in part this difference in expression levels is determined by cis-acting sequences. The dpp locus of E. coli was cloned. The first gene in the operon, dppA, encodes a periplasmic dipeptide-binding protein (DBP) required for dipeptide transport and chemotaxis. Downstream of dppA are other genes required for transport but not for chemotaxis. The dipeptide-binding protein was found to share 26.5% sequence identity with the periplasmic oligopeptide-binding protein OppA.

Amino Acid Sequence↗
PubMed1991

Magnesium transport in Salmonella typhimurium: the influence of new mutations conferring Co2+ resistance on the CorA Mg2+ transport system.

The CorA Mg2+ transport system of Salmonella typhimurium mediates both influx and efflux of Mg2+. Mutations at the corA locus (83.5 min) confer resistance to Co2+. Using transposon mutagenesis, three additional Co2+ resistance loci (corB, corC, and corD) were found and mapped to 55, 15, and 3min, respectively, on the S. typhimurium chromosome. No mutations corresponding to the reported corB locus at 95 min in Escherichia coli were obtained. The corB, corC, and corD mutations confer levels of Co2+ resistance intermediate between those of the wild-type and corA mutations. Isogenic strains were constructed containing combinations of transposon insertion mutations in each of the three Co(2+)-resistance loci to assess their influence on the CorA Mg2+ transport system. The Vmax and Km values for 28Mg2+ or for 57Co2+ and 63Ni2+ influx, analogues of Mg2+ transported by the CorA system, were changed less than twofold compared with the wild-type values, regardless of the mutation(s) present. However, while efflux of 28Mg2+ through the CorA system was decreased threefold in strains carrying one or two mutant alleles among corB, corC, or corD, efflux was completely abolished in either a corA or a corBCD strain. Thus, although the corA gene product is necessary and sufficient to mediate Mg2+ influx, Mg2+ efflux requires the presence of a wild-type allele of at least one of the corB, corC or corD loci.

Bacterial Proteins↗
PubMed1976

Responses of single units in the cat cochlear nucleus to sinusoidal amplitude modulation of tones and noise: linearity and relation to speech perception.

Responses to the sinusoidal modulation envelopes of amplitude-modulated tonend noise carriers were recorded from single units in the cochlear nucleus of the cat. The unit discharges were synchronized to the peaks of the modulation envelope. Population-averaged firing rate were independent of the modulation index of the stimulus. Temporal firing patterns, as represented by the shapes and magnitudes of modulation-cycle histograms, were strongly dependent on stimulus intesity and modulation index. Nonlinear nonsinusoidal responses to sinusoidal modulation envelopes were observed, but only at high values of sound intensity. These and other results are discussed in the context of psychological studies concerning the perception of speech information.

Acoustic Stimulation↗