PubMed Health⌕ Search

Biomedical subjects

M Hilmen

Publications and source records attributed to M Hilmen.

6 recordsLinked to original sources
PubMed1988

Flagellar dynamometer controls swarmer cell differentiation of V. parahaemolyticus.

Swarmer cell genes, laf, are induced when V. parahaemolyticus is grown on the surface of solidified media, embedded in solidified media, suspended in viscous media, or agglutinated with antibody in liquid media. These conditions have in common the constraint of the movement of the polar flagellum. To test the hypothesis that the polar flagellum functions as a sensor necessary for control of swarmer cell formation, we have constructed a variety of mutations in genes encoding components of the polar flagellum, fla. The consequence of such mutations is the constitutive expression of laf genes. So, the performance of the polar flagellum is coupled to the transcription of laf genes such that when function is perturbed, either physically or genetically, swarmer cell genes are induced. Because the polar flagellum appears to be capable of sensing external forces influencing its motion, we suggest it is acting as a dynamometer.

Culture Media↗
PubMed1979

Phase variation in Salmonella: genetic analysis of a recombinational switch.

The alternative expression of Salmonella genes H1 and H2, which specify different flagellar antigens, results in the oscillation of phenotype known as phase variation. This alternation is controlled by the inversion of an 800-base-pair sequence of DNA adjacent to, or including part of, the H2 gene. The invertable region was presumed to regulate the function of a promoter and to include specific sites at which a recombinational event, resulting in the inversion, could occur. Here we report genetic manipulations of hybrid lambda phage carrying the H2 gene that were used to define the H2 promoter region and the recombinational sites. The H2 gene fragment was inserted on a hybrid lambda phage next to the cheW gene, which lacked a promoter element. In the resulting fusion, cheW gene activity was restored, the expression of the H2 and cheW genes was controlled coordinately by the inversion, and the polarity of transcription and location of the H2 gene could be determined. Evidence from this type of gene fusion suggested that the H2 gene promoter is included in the inversion region. Hybrid H2 phage were constructed that contained substitutions for regions of the H2 gene. In contrast to hybrid lambda containing the H2 gene, which alternate between "on" and "off" states, several substituted lambdaH2 were fixed in the "on" state. A site necessary for the recombinational event must have been removed in these fixed lambdaH2.

Bacterial Proteins↗
PubMed1978

Regulation of gene expression by site-specific inversion.

A site-specific inversion event is responsible for phase transition in Salmonella, as indicated by heteroduplex analysis of recombinant molecules carrying the gene coding for H2 flagellin in Salmonella. The inversion region corresponds to approximately 800 base pairs in length, and the inversion process does not appear to be dependent upon the E. coli RecA recombination pathway. Specific deletion derivatives of the cloned fragments no longer produce H2-specific flagella, effectively mapping the H2 gene within about 300 bp of the inversion region. Recombinant products of the hybrid molecules arose spontaneously, and they were used in the mapping of restriction sites within the inversion region. The restriction maps further demonstrate the extent and nature of the inversion.

Bacterial Proteins↗
PubMed1977

Recombinational switch for gene expression.

Flagellar antigens are specified by two genes, H1 and H2. The expression of these genes is regulated such that only one gene activity, or phase, is expressed at a given time. Molecular cloning techniques were used to isolate the segments of Salmonella DNA which contain these genetic loci. Heteroduplex analyses revealed an anomaly in the cloned fragment, that is, and apparent inversion, which was shown to be adjacent to the H2 gene. A correlation was demonstrated between the phase state of the H2 gene and the sequence of the adjacent segment. We propose that an inversion of this region is the phase-determining event in flagellar gene expression in Salmonella.

Antigens, Bacterial↗
PubMed1977

Characterization of lambda Escherichia coli hybrids carrying chemotaxis genes.

Molecular cloning techniques were used to construct hybrid Escherichia coli lambda phage and isolate Col E1 factors that carried the cheB region of the E. coli genome. The products of these genes were examined by using a series of deletions in the phage to stimulate specific polypeptide synthesis in ultraviolet-irradiated cells and by using Col factor to program protein synthesis in minicells. Seven flagellar related polypeptides were synthesized. Three of these with apparent molecular weights of 38,000, 28,000, and 8,000 were associated with the cheB region; three polypeptides 63,000, 61,000, and 60,000 were associated with the region that maps between cheB and cheA. These bands were referred to as the triplet group. We suggest that these polypeptides are the same as the methyl-accepting chemotaxis protein described by Kort et al. (Proc. Natl. Acad. Sci. U.S.A. 72:3939-3943, 1975). Another polypeptide with a molecular weight of 12,000 is associated with the cheA region which also produces at least three gene products. We conclude that the cheA-cheB region in E. coli is complex. Further genetic and biochemical analyses are required to describe all of these products.

Bacterial Proteins↗