摘要:

SummaryThere has been a recent revival of interest in one of the most abundantEscherichia coliproteins, H1 (also called H‐NS). This protein was first identified many years ago as a major component of the bacterial nucleoid, and has been characterized biochemically by several groups. However, no clear function for the protein emerged from these studies. Our thinking has been transformed by recent findings which complement the biochemistry with genetic data. Several mutations, selected over many years by virtue of their diverse effects on gene expression, have turned out to be allelic and to fall within the structural gene for H1. Bringing together the genetics and the biochemistry has demonstrated that the whole is worth more than the sum of the parts! These findings have far‐reaching implications for the mechanisms by which gene expression is regulated and also, perhaps, for the control of bacterial virule

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00559.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryYeast cells produce a set of enzymes which are involved in the metabolism of phosphate, and include acid and alkaline phosphatases as well as permeases. Most of these enzymes are synthesized in response to the presence or absence of inorganic phosphate. In the past few years a considerable amount of genetic and molecular evidence has accumulated and a rather precise overall picture emerges which describes the mechanism of phosphate control at the level of gene activation. This mini‐review summarizes these data. The main focus lies on the regulatory features associated with the control of transcription ofPH05, a gene coding for most of the regulated acid phosphatase activity produced by yeast cell

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00560.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryTonB protein serves as an energy transducer to couple cytoplasmic membrane energy to high‐affinity active transport of iron siderophores and vitamin B12across the outer membranes of Gram‐negative bacteria. The biochemical mechanism of the energy transduction remains to be determined, but important details are already known. TonB is targeted to and anchored in the cytoplasmic membrane by a single membrane‐spanning domain and spans the periplasm to physically interact with outer‐membrane receptors of the transport ligands. TonB‐dependent energy transduction is modulated by ExbB protein, which stabilizes TonB, and possibly by several other proteins including ExbC, ExbD, and TolQ. TonB has a relatively short functional half‐life that is accelerated when rates of active transport across the outer membrane are increased. A model that incorporates this information, as well as some tempered speculation, i

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00561.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryCells ofEscherichia colipossess high‐affinity active transport systems of vitamin B12and iron‐siderophore complexes. Specific outer‐membrane proteins carry out the energy‐dependent transport across the outer membrane, in conjunction with the TonB coupling protein. Mutagenesis experiments have identified a conserved region near the amino‐terminus of the outer‐membrane transporters that is necessary for energy‐coupled transport. The ability of extragenic suppressor mutations intonBto correct the transport defect indicates that TonB couples the proton‐motive force to the outer‐membrane proteins

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00562.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryUncharged tRNA has been shownin vivoto have an active role both in the stringent response, and in modulating the rate of translational elongation. Both of these effects appear to be mediated by codon–anticodon interactions on the ribosome. Although the involvement of uncharged tRNA in the stringent response was expected fromin vitroexperiments, it has only recently been confirmedin vivo.Inhibition of translation by cognate uncharged tRNA was not expected, and a model is proposed in which excess uncharged tRNA competes with charged tRNA (in ternary complex) for the 30S component of the ribosomal A site. When uncharged tRNA is in sufficient excess over charged tRNA, interaction of uncharged tRNA with the 50S component of the A site occurs as well, leading to a stringent response. The cell has a continuum of responses to decreasing aminoacyl‐tRNA levels: in moderately limited conditions, the proportion of uncharged tRNA increases, and the translation rate is slowed; under more severe limitations, uncharged tRNA provokes a stringent response, with pleiotropic consequences for the c

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00563.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe DNA sequence of the K99fanFgene, encoding FanF, was determined. An open reading frame of 999bp was found. The primary structure of FanF was deduced and analysis revealed the presence of a signal sequence of 22 amino acid residues. The mature protein contains 311 amino acid residues (Mr33905 D). The amino acid sequence of FanF showed similarity with the K88ab major subunit FaeG.A specific mouse antiserum against FanF was prepared by constructing and purifying a hybrid CroLacZ‐FanF protein. Minicell analysis, immunoblotting and immunoelectronmicroscopy revealed a pool of FanF in the periplasm of K99‐producing cells and showed, furthermore, that FanF Is a minor component of K99 fibrillae, present at the top and in or along the shaft of the K99 fibrillar structures.AfanFmutant plasmid was constructed. Cells harbouring this plasmid produced all K99‐specific proteins, except FanF, but produced 0.1% of the K99 fibrillae relative to ‘normal’ K99‐producing cells. Electron microscopic observations showed that cells defective infanFproduce only a few (apparently short) K99 fibrillae. FanF, therefore, was supposed to play a role in initiation and elongation of K99 fibrillae formation.Thin‐layer chromatography experiments involving purified receptor material showed that FanF is not required for binding of K99 fibrillae to the ganglioside receptor. Fibrillae produced by an adhesion‐negative strain carrying a mutation in the K99 major fibrillar subunit were shown to contain a normal

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00564.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryResistance to intercalating dyes (ethidium, acriflavine) and other organic cations, such as quaternary ammonium‐type antiseptic compounds, mediated by theStaphylococcus aureusptasmid pSK1 is specified by an energy‐dependent export mechanism encoded by theqacAgene. From nucleotide sequence analysis,qacAis predicted to encode a protein ofMr55017 containing 514 amino acids. The gene is likely to initiate with a CUG codon, and a 36bp palindrome immediately precedingqacA, along with an upstream reading frame with homology to the TetR repressors, may be components of a regulatory circuit. The putative polypeptide specified byqacAhas properties typical of a cytoplasmic membrane protein, and is indicated to be a member of a transport protein family that includes proteins reponsible for export‐mediated resistance to tetracycline and methylenomycin, and uptake of sugars and quinate. The analysis suggests thatN‐ andC‐terminal regions of these proteins are involved in energy coupling (proton translocation) and substrate transport, respectively. The last common ancestor of theqacAand relatedtet(tetracycline resistance) lineages is inferred to have been repressor controlled, as occurs for moderntetdeterminants from Gram‐negative, but not those from Gram‐posit

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00565.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryStudies of the equilibrium between native and denatured forms of wild‐type levansucrase showed that the denatured form was predominant at 37°C and pH 7 in the absence of free metal. The shift to the native form was promoted by metal ions such as Fe3+or Ca2+. This metal‐dependent refolding process was not observed in levansucrase variants bearing the amino acid substitution Gly‐366→Asp or Gly‐366→Val. These variants were only slightly secreted byBacillus subtilisalthough their signal sequences were normally cleaved and their exocellular forms stable. In contrast, the Gly‐366→Ser variant was secreted at near‐normal levels and shared a part of thein vitrorefolding properties of the wild‐type protein. These differential properties might be related to the ability of the altered region to form a β‐turn structure.We discuss the possible role of metal ions in the coupling of protei

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00566.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe DNA repeat region offcrA76, the gene encoding a group A streptococcal Fc‐binding protein, was sub‐cloned in‐frame into anEscherichia coliplasmid expression vector. The expressed protein product displayed the same Fc‐binding properties as the full‐length Fc‐binding protein expressed fromfcrA76.The affinity‐purified, full‐length Fc‐binding protein was found to compete with staphylococcal protein A or streptococcal protein G for binding to beads coated with human IgG. These results are consistent with earlier studies suggesting that the binding sites on human IgG for protein A, protein G and the type II Fc‐binding protein from group A streptococci are located at the interface of the CH2and CH3domai

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00567.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe budding yeastSaccharomyces cerevisiaehas a finite life span that is defined by the number of times the cell divides. The patterns of expression of certain genes change in a specific manner during the life span, implying that at least some of the manifestations of the ageing process are subject to gene regulation. It has now been determined that the controlled expression of theRASoncogene in yeast increases the longevity of this organism, indicating that, conversely, a defined alteration in the activity of a single gene can extend this organism's life span. The results suggest that there is a balance between life‐span extension and growth arrest whenRASis expressed. Inasmuch as the homologues ofRASin yeast function to integrate cell metabolism with the cell cycle, these studies raise the possibility that this integrative function may also apply to the co‐ordination of successive cell cycles during the life s

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00568.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY