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Biomedical subjects

M Silverman

Publications and source records attributed to M Silverman.

At least 433 records · Page 24Linked to original sources
PubMed1974

Positioning flagellar genes in Escherichia coli by deletion analysis.

Two methods were devised to select a series of overlapping deletion mutations carried on episomal elements in Escherichia coli. The deletions were then used in an analysis of (i) the relative position on the genome of previously described mutant loci in the flagellar genes, (ii) the relative position of a newly defined cistron, flaN, and (iii) the orientation and direction of transcription of genes previously assigned to multicistronic transcriptional units. As a result of this analysis and previous work, we report the following arrangement of the flagellar genes in the his-aroD region of the E. coli genetic map: his-flaR-flaQ-flaP-flaA-flaE-flaO-flaC-flaB-flaN-hag-flaD-uvrC-flaI-mot- flaG-flaH. The genes flaA, P, Q, and R, flaB, C, O and E, and flaG and H are co-transcribed in that order.

Chromosome Mapping↗
PubMed1974

Assembly of hybrid flagellar filaments.

The distribution of flagellin subunits in flagellar filaments synthesized by merodiploid strains carrying two distinguishable hag loci has been examined. The filament was found to be a homogeneous co-polymer of the two subunits. This suggests that the subunits may be able to mix freely before being assembled.

Antigens, Bacterial↗
PubMed1974

Characterization of Escherichia coli flagellar mutants that are insensitive to catabolite repression.

In Escherichia coli, the synthesis of the flagellar organelle is sensitive to catabolite repression. Synthesis requires the presence of the cyclic adenosine monophosphate receptor protein (Crp) and 3',5'-cyclic adenosine monophosphate (cAMP); i.e., mutants that lack Crp or adenylcyclase (Cya) synthesize no flagella. We isolated and characterized a series of mutants (cfs) that restored flagella-forming ability in a Crp strain of E. coli. The mutations in these strains were transferred onto episomes and they were then introduced into a variety of other strains. The presence of the mutation resulted in flagella synthesis in Cya and Crp strains as well as in the wild type grown under conditions of catabolite repression. Deletion analysis and other genetic studies indicated that: (i) the cfs mutations had a dominant effect when they were in the transconfiguration in merodiploids: (ii) they occurred in or very close to the flaI gene: and (iii) their expression required the presence of an intact flaI gene adjacent to the cfs mutation. Biochemical studies showed that the synthesis of at least two flagellar polypeptides, the hook subunit and an amber fragment of flagellin, were absent in strains that carried a cya mutation. Their synthesis was depressed in strains grown under conditions of catabolite repression. The presence of the cfs mutation restored the specific synthesis of these two polypeptides. We suggest that the formation of the flaI gene product is the step in flagellar synthesis that is catabolite sensitive and requires cAMP. We propose a regulatory function for the product of the flaI gene.

Adenylyl Cyclases↗
PubMed1973

Bilateral nephrectomy for massive pulmonary hemorrhage in Goodpasture's syndrome.

A case of Goodpasture's syndrome is described in which bilateral nephrectomy was undertaken because of massive pulmonary hemorrhage. Similar cases recorded in the literature are reviewed. Various hypotheses to explain the beneficial effects of renal ablation on lung purpura are considered. It is suggested that the pulmonary hemorrhage in Goodpasture's syndrome is mediated in part by a non-antibody humoral factor with permeability-increasing properties that is released from the nephritic kidney.

Adolescent↗
PubMed1973

Genetic analysis of flagellar mutants in Escherichia coli.

Flagellar mutants in Escherichia coli were obtained by selection for resistance to the flagellotropic phage chi. F elements covering various regions of the E. coli genome were then constructed, and, on the basis of the ability of these elements to restore flagellar function, the mutations were assigned to three regions of the E. coli chromosome. Region I is between trp and gal; region II is between uvrC and aroD; and region III is between his and uvrC. F elements carrying flagellar mutations were constructed. Stable merodiploid strains with a flagellar defect on the exogenote and another on the endogenote were then prepared. These merodiploids yielded information on the complementation behavior of mutations in a given region. Region III was shown to include at least six cistrons, A, B, C, D, E, and F. Region II was shown to include at least four cistrons, G, H, I, and J. Examination of the phenotypes of the mutants revealed that those with lesions in cistron E of region III produce "polyhooks" and lesions in cistron F of region III result in loss of ability to produce flagellin. Mutants with lesions in cistron J of region II were entirely paralyzed (mot) mutants. Genetic analysis of flagellar mutations in region III suggested that the mutations located in cistrons A, B, C, and E are closely linked and mutations in cistrons D and F are closely linked.

Antigens, Bacterial↗
PubMed1973

Genetic analysis of bacteriophage Mu-induced flagellar mutants in Escherichia coli.

In previous work, at least 10 discrete cistrons involved in the synthesis of flagella in Escherichia coli were described. Six cistrons were located between his and uvrC on the genetic map. These were referred to as hag, flaA, flaB, flaC, flaD, and flaE. Four cistrons referred to as mot, flaG, flaH, and flaI were located between uvrC and aroD. In order to determine whether these genes are organized into transcriptional units, a series of Mu phage-induced flagellar mutants was studied. The mutant strains behaved as if they were carrying strong polar mutations. Of 228 independent Mu-induced mutants, 114 with mutations in the his-aroD region of the genetic map were tested by preparing partial diploid strains with episomes carrying a variety of previously defined mutations. The pattern of complementation that emerged indicated that cistrons flaB, flaC, and flaE form a transcriptional unit. Cistron flaO, defined in the course of this study, is also a member of this transcriptional unit. The order of transcription is B-C-O-E. flaA was found to be complex, and it included four cistrons, flaA, flaP, flaQ, and flaR, with the transcriptional order A-P-Q-R. Cistrons flaG and flaH are cotranscribed with the transcriptional order G-H. The remaining genes, flaD, flaI, hag, and mot do not belong to multicistronic transcriptional units. Complementation analysis suggested that the cheC locus is the same as cistron flaA.

Chromosome Mapping↗
PubMed1973

Brush border disaccharidases in dog kidney and their spatial relationship to glucose transport receptors.

The localization of disaccharidases in kidney has been studied by means of the multiple indicator dilution technique. A pulse injection of a solution containing Evans blue dye (plasma marker), creatinine (extracellular marker), and a (14)C-labeled disaccharide (lactose, sucrose, maltose, and alphaalpha-trehalose), is made into the renal artery of an anesthetized dog, and the outflow curves are monitored simultaneously from renal venous and urine effluents. Lactose and sucrose have an extracellular distribution. Trehalose and maltose remain extracellular from the postglomerular circulation. About 75% of filtered tracer maltose or trehalose is extracted by the luminal surface of the nephron. Thin-layer chromatography of urine samples shows that all of the excreted (14)C radiolabel is in the form of the injected disaccharide. Following the administration of phlorizin, all of the filtered radioactivity is recoverable in the urine, but chromatography of the urine samples now reveals that there is a significant excretion of [(14)C]glucose, approximating the amount previously extracted under control conditions (in the absence of phlorizin). It has been verified that no hydrolysis of maltose or trehalose to their constituent glucose subunits occurred during the transit of tracer between the point of injection (renal artery), and the point of filtration (glomerular basement membrane). Similarly, after addition of [(14)C]disaccharides to fresh urine there is no chromatographically recoverable [(14)C]glucose. It is concluded that there exist alpha-glucosidases with maltase and trehalase activity along the brush border of the proximal tubule and that these disaccharidases are located spatially superficial to the glucose transport receptors.

Animals↗