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  • 1
    Electronic Resource
    Electronic Resource
    Alkaline phosphatase which lacks its own signal sequence becomes enzymatically active when fused to N-terminal sequences of Escherichia coli haemolysin (HlyA) (1987)
    Springer
    Molecular genetics and genomics 208 (1987), S. 88-93 
    Details
    ISSN: 1617-4623
    Keywords: Protein transport ; Haemolysin ; TnphoA insertion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Fusion of the alkaline phosphatase gene (phoA) which lacks its own signal peptide sequence to the N-terminal region of hlyA, the structural gene for Escherichia coli haemolysin, leads to active alkaline phosphatase (AP). AP activity depends on the length of the N-terminal region of hlyA. An optimum is reached when 100–200 amino acids of HlyA are fused to PhoA but fusion of as little as 13 amino acids of HlyA to PhoA is sufficient to yield appreciable AP activity. When cells are treated with lysozyme most of the AP activity is found associated with the membrane fraction but a substantial amount is also found in the soluble fraction, most of which may represent, a periplasmic pool of AP. The soluble portion of AP activity is significantly increased when the cells are disrupted by ultrasonication, which indicates that the fusion proteins are only loosely associated with the membrane and that large parts are already located on the outside of the cytoplasmic membrane. The expected fusion proteins were identified in the soluble and the membrane fractions and their amounts in these fractions correlated well with AP activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330427
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  • 2
    Electronic Resource
    Electronic Resource
    Characterization of a sequence (hlyR) which enhances synthesis and secretion of hemolysin in Escherichia coli (1988)
    Springer
    Molecular genetics and genomics 212 (1988), S. 76-84 
    Details
    ISSN: 1617-4623
    Keywords: Escherichia coli hemolysin ; Regulation ; hlyR ; Enhancement of hemolysin expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A sequence (hlyR) of about 600 bp which enhances the expression of hemolysin (HlyA) more than 50-fold was identified in the plasmid pHly152-specific hemolysin (hly) determinant. Deletion of this entire hlyR sequence led to the same low level of hemolysin synthesis and excretion as that expressed by the recombinant plasmid pANN202-312. HlyR was active in cis but its activity was orientation-dependent. The enhancing sequence, hlyR, is separated from the promoter phlyI transcribing hlyC, hlyA and possibly hlyB by more than 1.5 kb including an IS2 element. Stepwise removal of the hlyR sequence from its 5′ end by exonuclease III (ExoIII) digestion yielded several types of deletion mutants which expressed decreasing amounts of hemolysin. A similar observation was made when hlyR was shortened by ExoIII from its 3′ end, which suggests that more than one functional region may be present in the hlyR sequence. A deletion of 717 bp within the adjacent IS2 element reduced the activity of hlyR only slightly, indicating that IS2 is not directly involved in the enhancement mechanism but that it may support an optimal positioning in hlyR relative to the hly promoter. The nucleotide sequence of hlyR is rich in A+T and does not contain an extended open reading frame, but exhibits several sequence motives that may represent sites for protein binding and DNA bending.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00322447
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  • 3
    Electronic Resource
    Electronic Resource
    Mutations affecting activity and transport of haemolysin in Escherichia coli (1987)
    Springer
    Molecular genetics and genomics 206 (1987), S. 238-245 
    Details
    ISSN: 1617-4623
    Keywords: E. coli ; Haemolysin ; Mutants ; Functional domains of HlyA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Temperature-sensitive mutants that exhibit an altered haemolytic phenotype were isolated from Escherichia coli harbouring the plasmid pHly152. Complementation with recombinant plasmids carrying one of the four hly genes (C, A, B or D) allowed localization of the hly ts mutations. A ts mutation in hlyC leads to a pro→leu exchange in amino acid position 53 of HlyC. Two ts mutations in HlyA were found in positions 312 (ser→pro) and 315 (thr→ile). Both amino acid exchanges are located in the same hydrophobic domain of HlyA which extends from amino acids 299 to 327. Two different mutations were introduced by site-specific mutagenesis in this hlyA domain: one by an exchange of ala, val to asp, glu (positions 313, 314) altering the hydrophobicity of this region and another which removes most of this hydrophobic portion. Both mutants have entirely lost the haemolytic activity but the mutant haemolysins are still efficiently transported across both membranes when hlyB and hlyD are provided. Functional HlyC is not required for the transport of the mutant haemolysins. Two site-specific mutations at the N-terminal end of hlyA (one at amino acid position 2 leading to a thr→pro exchange and another deleting ile and thr at positions 4 and 5) also do not affect the transport of the altered haemolysins. The thr→pro exchange enhances the haemolytic activity of the corresponding mutant, whereas the ile, thr deletion exhibits little or no effect on the haemolytic activity. Removal of the last 37 amino acids from the C-terminal end of HlyA leads to a truncated haemolysin which retains its haemolytic activity but is not secreted by the HlyB and HlyD transport system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333579
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  • 4
    Electronic Resource
    Electronic Resource
    Expression and regulation of the plasmid-encoded hemolysin determinant of Escherichia coli (1984)
    Springer
    Molecular genetics and genomics 197 (1984), S. 196-203 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary As a first approach towards studying the regulation of hemolysin synthesis in Escherichia coli, we have fused lacZ into the four hly genes (hlyC, hlyA, hlyB a and hlyB b) using the Mud-1 (Mu::lacZ, Y, Apr) phage. The sites of insertion of Mud-1 within the various hly genes of the Hly plasmid pHly152 were determined by the hemolytic phenotype of the Hly- mutants (Hly ex - /Hly in - or Hly ex - /Hly in + ) and by complementation of these Hly- mutants with recombinant plasmids carrying cloned hly genes. It was found that hlyC, hlyA and hlyB a are transcribed from a relatively weak promoter (hlypL) located in front of hlyC. The activity of β-galactosidase is considerably lower when Mud-1 is integrated in hlyB a than when it is inserted in hlyC, suggesting a considerable decline in hly gene expression from hlyC to hlyB a. The DNA sequence upstream of the coding region of hlyC was found to promote galK gene expression when a fragment covering this region was inserted into the promoter-probe vector pKO-11. A putative promoter sequence, which could correspond to hlypL, was identified in this sequence. The hlyB b gene appears to be transcribed from a different promoter and the direction of transcription seems to be opposite to that of the hlyC, A, B a operon. The strength of this promoter (hlypR), based on the level of β-galactosidase activity of Mud-1 insertion mutants in hlyB b, is considerably higher than that of hlypL. The hly::lacZ fusions were also used to study a possible regulatory control of the hly genes on the transcriptional level by various physiological conditions (cAMP, media composition, growth phase), which have been shown to affect the synthesis of hemolysin. It was found that none of these conditions influence the expression of β-galactosidase, ruling out the possibility that transcription of the hly genes is modulated by these conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330963
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