Biomedical subjects

M I Simon

Publications and source records attributed to M I Simon.

243 records · Page 14Linked to original sources

PubMed1971

Purification and partial characterization of Bacillus subtilis Flagellar hooks.

A method for preparing bacterial flagellar hook structures is described. The method involves isolating intact flagella from a mutant which makes thermally labile flagellar filaments and heat-treating them to disaggregate the filament preferentially. The resulting hook preparation can be separated and purified by velocity and isopycnic centrifugation. The purified hooks sediment at a relative S value of 77. On acrylamide gel electrophoresis in sodium dodecyl sulfate, they show one major and a number of minor protein bands. The purified hooks can be used to immunize rabbits, and the resulting antiserum is hook-specific. These results support the notion that hooks are composed of a protein that differs from flagellin.

Animals↗

PubMed1971

Division mutants of Bacillus subtilis: isolation and PBS1 transduction of division-specific markers.

A procedure for the isolation of Bacillus subtilis mutants that appear to be defective in septum synthesis has been described. Fourteen mutants isolated with this technique were found to be located at four distinct loci on the B. subtilis chromosome. These have been designated divA, divB, divC, and divD. The four mutants in the divA group synthesize septa; however, they do so with a high frequency of error resulting in minicell production. Mapping data were obtained by scoring cotransduction frequencies using PBS1-transducing lysates. Thus, some of the genes apparently involved in septum synthesis and their order on the genome have been established. The results of a study by electron microscope of some of the mutants is also presented.

Bacillus subtilis↗

PubMed1970

Bacterial flagella: polarity of elongation.

Newly synthesized regions of Bacillus subtilis flagella were labeled with fluorophenylalanine or [(3)H]leucine. The flagella were then examined for altered gross morphology or by radioautography. Results of both experiments indicate that flagella elongate in vivo by polymerization of flagellin subunits onto the distal end of the filament.

Antigens↗

PubMed1969

Synthesis of bacterial flagella. II. PBS1 transduction of flagella-specific markers in Bacillus subtilis.

The linkage relationship of mutants involved in the synthesis of flagella was determined by PBSl transduction. Mutants that affect the structure of flagellin (hag) and temperature-sensitive mutants (flaTS) that produce flagella when grown at 37 C but not when grown at 46 C were examined. All of the mutants were found to be linked to the hisA1 marker. The flaTS mutants fell into three clusters. Group A contained the majority of mutants which were loosely grouped around the hag locus. Group B mutants were segregated from the hag locus and appeared closely linked to the phage adsorption site gene (gtaA), and group C was only loosely linked to hisA1 and thus far contains only one mutant. A flagella locus (ifm) affecting both the degree of motility and level of flagellation was shown to map near group A. Mutants affecting motility (mot) were not linked to hisA1 by PBSl transduction. Several markers previously shown to link to hisA1 were ordered with respect to hisA1 and the flagellar genes.

Antigens↗

PubMedDate not supplied

Protein phosphorylation in the bacterial chemotaxis system.

Bacterial chemotaxis involves the detection of changes in concentration of specific chemicals in the environment of the cell as a function of time. This process is mediated by a series of cell surface receptors that interact with and activate intracellular protein phosphorylation. Five cytoplasmic proteins essential for chemotaxis have been shown to be involved in a coupled system of protein phosphorylation. Ligand binding to cell surface receptors affects the rate of autophosphorylation of the CheA protein. In the absence of an attractant bound to receptor and in the presence of the CheW protein, the rate of CheA autophosphorylation is markedly increased. Phosphorylated CheA can transfer phosphate to the CheY or CheB proteins; phosphorylation of these "effector" proteins may increase their activity. The CheY protein is thought to regulate flagellar rotation and thus control swimming behavior. The CheB protein modifies the cell surface receptor and thus regulates receptor function. Finally, another chemotaxis protein, CheZ, acts to specifically dephosphorylate CheY-phosphate. This system shows marked similarity to the 2-component sensor-regulator systems found to control specific gene expression in a variety of bacteria.

Bacteria↗

PubMedDate not supplied

Structure of the serine chemoreceptor in Escherichia coli.

Many biological processes depend on the function of proteins that detect changes in a cell's environment and transmit the information to the cytoplasm, for example, peptide hormone receptors. In Escherichia coli this class of proteins is exemplified by the sensory transducers (also called signalling proteins or methyl-accepting chemotaxis proteins) which have a central role in mediating chemotactic behaviour. The sensory transducers are the products of four genes: tsr, tar, tap and trg. Each transducer detects changes in the environmental concentration of one or a very few attractants: Tsr, serine; Tar, aspartate and maltose; Tap, unknown; and Trg, ribose and galactose. Tsr and Tar act directly as chemoreceptors for the amino acid attractants and signal changes in their degree of occupancy to the flagellar apparatus. Detection of these changes in occupancy is made possible as the transducers are methylated at multiple glutamate residues such that their level of methylation reflects the most recent chemoeffector concentration. Biochemical and genetic information concerning the serine transducer protein has been accumulating rapidly but little is known about the structure of the molecule. We present here the nucleotide sequence of the tsr gene of E. coli; the amino acid sequence derived from it suggests that the Tsr transducer protein has a relatively simple transmembrane structure that may place limits on the mechanisms available for the transmission of sensory information into the cell.

Amino Acid Sequence↗

PubMedDate not supplied

Chromosomal sublocalization of human c-myb and c-fes cellular onc genes.

The transforming genes of acutely transforming retroviruses are derived from conserved cellular genes (c-onc genes) which are believed to be important in normal cell growth and differentiation. Recent studies indicate that altered expression of c-onc genes, for example, by insertion of viral genomes, gene amplification or chromosomal translocation, can lead to development of malignant diseases in man and animals. c-myb and c-fes are homologues of the transforming genes of avian myeloblastosis virus and feline sarcoma virus (Gardner and Snyder-Theilen strains), respectively. c-myb is transcribed preferentially in immature haematopoietic cells and probably codes for a protein important in differentiation of these cells. The viral fes gene, like several other viral onc genes, encodes a tyrosine-specific protein kinase. However, c-fes transcripts have not been detected in the types of human cells examined so far. c-myb and c-fes have been assigned to human chromosomes 6 and 15, respectively. Specific aberrations involving these chromosomes have been observed at high frequency in several human neoplasms. We have now sublocalized c-myb to 6q22-24 and c-fes to 15q25-26 by in situ hybridization of the human c-onc probes to human mitotic chromosome preparations. These chromosomal segments are indeed involved in nonrandom translocations in several human tumours. The results encourage further investigation into the role of onc genes in the pathogenesis of specific neoplasms.

Chromosome Aberrations↗

PubMedDate not supplied

Transposition of structural genes to an expression sequence on a linear plasmid causes antigenic variation in the bacterium Borrelia hermsii.

In Borrelia hermsii, a spirochaete that causes relapsing fever, the switch between expression of two frequent variable major protein (VMP) types (7 and 21) is associated with a DNA rearrangement. Both cell types 7 and 21 contain untranscribed 7 and 21 VMP genes on linear plasmids. The serotype 7 cells contain an additional copy of the 7 VMP gene fused to an expression sequence on another linear plasmid. Switching to the 21 serotype involves removal of the transcribed 7 VMP gene and fusion of a copy of the 21 VMP gene to this same expression sequence. Thus recombination between linear plasmids can activate different VMP genes.

Bacterial Proteins↗

PubMedDate not supplied

Spatial relationship of the Fis binding sites for Hin recombinational enhancer activity.

Site-specific recombination reactions involve the joining or rearrangement of discrete DNA segments in a highly precise manner. A site-specific DNA inversion regulates the expression of flagellin genes in Salmonella by switching the orientation of a promoter. Analysis of the reaction has shown that, in addition to DNA sequences at the two boundaries of the 1-kilobase invertible segment where strand exchange occurs, another cis acting sequence is required for efficient inversion. This 60-base-pair enhancer-like sequence can function at many different locations and in either orientation in a plasmid substrate. It includes two binding sites for a host protein called Factor II or Fis (refs 4 and 5). Here we have investigated the importance of the spatial relationship between the two Fis binding sites for enhancer activity and have found that the correct helical positioning of the binding sites on the DNA is critical. However, this result could not be accounted for by effects on Fis binding. We propose a model for enhancer function in which the enhancer region acts to align the recombination sites into a specific conformation required for productive synapsis.

Bacterial Proteins↗