Biomedical subjects

Issar Smith

Publications and source records attributed to Issar Smith.

22 records · Page 2Linked to original sources

PubMed2002

Novel Mycobacterium tuberculosis anti-sigma factor antagonists control sigmaF activity by distinct mechanisms.

The aetiological agent of tuberculosis, Mycobacterium tuberculosis, encodes 13 sigma factors, as well as several putative anti-, and anti-anti- sigma factors. Here we show that a sigma factor that has been previously shown to be involved in virulence and persistence processes, sigmaF, can be specifically inhibited by the anti-sigma factor UsfX. Importantly, the inhibitory activity of UsfX, in turn, can be negatively regulated by two novel anti-anti-sigma factors. The first anti-anti-sigma factor seems to be regulated by redox potential, and the second may be regulated by phosphorylation as it is rendered non-functional by the introduction of a mutation that is believed to mimic phosphorylation of the anti-anti-sigma factor. These results suggest that sigmaF activity might be post-translationally modulated by at least two distinct pathways in response to different possible physiological cues, the outcome being consistent with the bacteria's ability to adapt to diverse host environments during disease progression, latency and reactivation.

Amino Acid Sequence↗

PubMed2002

Mycobacterium tuberculosis genes induced during infection of human macrophages.

We identified Mycobacterium tuberculosis genes preferentially expressed during infection of human macrophages using a promoter trap adapted for this pathogen. inhA encodes an enoyl-acyl carrier protein reductase that is required for mycolic acid biosynthesis (A. Quemard et al., Biochemistry 34:8235-8241, 1995) and is a major target for isoniazid (INH) in mycobacterial species (A. Banerjee et al., Science 263:227-230, 1994). Since overexpression of inhA confers INH resistance in Mycobacterium smegmatis (Banerjee et al., Science 263:227-230, 1994), we designed a promoter trap based on this gene. A library of clones, containing small fragments of M. tuberculosis DNA cloned upstream of inhA in a plasmid vector, was electroporated into M. tuberculosis, and the resulting culture was used to infect the human monocytic THP-1 cell line. Selection was made for clones surviving INH treatment during infection but retaining INH sensitivity on plates. The DNA upstream of inhA was sequenced in each clone to identify the promoter driving inhA expression. Thirteen genes identified by this method were analyzed by quantitative reverse transcription-PCR (R. Manganelli et al., Mol. Microbiol. 31:715-724, 1999), and eight of them were found to be differentially expressed from cultures grown in macrophages compared with broth-grown cultures. Several of these genes are presumed to be involved in fatty acid metabolism; one potentially codes for a unique DNA binding protein, one codes for a possible potassium channel protein, and the others code for proteins of unknown function. Genes which are induced during infection are likely to be significant for survival and growth of the pathogen; our results lend support to the view that fatty acid metabolism is essential for the virulence of M. tuberculosis.

Bacterial Proteins↗

PubMed2002

ideR, An essential gene in mycobacterium tuberculosis: role of IdeR in iron-dependent gene expression, iron metabolism, and oxidative stress response.

The mycobacterial IdeR protein is a metal-dependent regulator of the DtxR (diphtheria toxin repressor) family. In the presence of iron, it binds to a specific DNA sequence in the promoter regions of the genes that it regulates, thus controlling their transcription. In this study, we provide evidence that ideR is an essential gene in Mycobacterium tuberculosis. ideR cannot normally be disrupted in this mycobacterium in the absence of a second functional copy of the gene. However, a rare ideR mutant was obtained in which the lethal effects of ideR inactivation were alleviated by a second-site suppressor mutation and which exhibited restricted iron assimilation capacity. Studies of this strain and a derivative in which IdeR expression was restored allowed us to identify phenotypic effects resulting from ideR inactivation. Using DNA microarrays, the iron-dependent transcriptional profiles of the wild-type, ideR mutant, and ideR-complemented mutant strains were analyzed, and the genes regulated by iron and IdeR were identified. These genes encode a variety of proteins, including putative transporters, proteins involved in siderophore synthesis and iron storage, members of the PE/PPE family, a membrane protein involved in virulence, transcriptional regulators, and enzymes involved in lipid metabolism.

Bacterial Proteins↗

PubMed2002

Postexponential regulation of sin operon expression in Bacillus subtilis.

The expression of many gene products required during the early stages of Bacillus subtilis sporulation is regulated by sinIR operon proteins. Transcription of sinIR from the P1 promoter is induced at the end of exponential growth. In vivo transcription studies suggest that P1 induction is repressed by the transition-state regulatory protein Hpr and is induced by the phosphorylated form of Spo0A. In vitro DNase I footprinting studies confirmed that Hpr, AbrB, and Spo0A are trans-acting transcriptional factors that bind to the P1 promoter region of sinIR. We have also determined that the P1 promoter is transcribed in vitro by the major vegetative sigma factor, final sigma(A), form of RNA polymerase.

Bacillus subtilis↗