<i>Escherichia coli hha</i> mutants, DNA supercoiling and expression of the haemolysin genes from the recombinant plasmid pANN202‐312

Carmona, Manuel; Balsalobre, Carlos; Muñoa, F.; Mouriño, Mercedes; Jubete, Yolanda; Cruz, Fernando de la; Juárez, Antonio

doi:10.1111/j.1365-2958.1993.tb01230.x

Cited by 48 publications

(66 citation statements)

References 31 publications

(8 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1). Deletion of hlyR results in an unnatural repression of hemolysin expression (4,42). This phenotype could be interpreted as being caused by the loss of the above mentioned ops element, but this has not yet been demonstrated.…”

mentioning

confidence: 99%

“…In addition to this as yet unclear antitermination mechanism, the hly operon is regulated by both temperature and osmolarity (29,30). Studies focused on the regulatory features of the hly operon of plasmid pHly152 led to the identification of the Hha protein (4,33) and to the finding that hha mutants are partially derepressed under conditions involving temperature-and osmolarity-mediated hemolysin repression. The Hha protein belongs to a new family of modulators, which includes, among others, the YmoA protein, a temperature-dependent modulator of the expression of different virulence factors in Yersinia enterocolitica (5).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Temperature- and H-NS-Dependent Regulation of a Plasmid-Encoded Virulence Operon Expressing Escherichia coli Hemolysin

et al. 2002

View full text Add to dashboard Cite

Proteins H-NS and Hha form a nucleoprotein complex that modulates expression of the thermoregulated hly operon of Escherichia coli. We have been able to identify two H-NS binding sites in the hly regulatory region. One of them partially overlaps the promoter region (site II), and the other is located about 2 kbp upstream (site I). In contrast, Hha protein did not show any preference for specific sequences. In vitro, temperature influences the affinity of H-NS for a DNA fragment containing both binding sites and H-NS-mediated repression of hly operon transcription. Deletion analysis of the hly regulatory region confirms the relevance of site I for thermoregulation of this operon. We present a model to explain the temperature-modulated repression of the hly operon, based on the experiments reported here and other, preexisting data.

show abstract

mentioning

confidence: 99%

mentioning

confidence: 99%

Temperature- and H-NS-Dependent Regulation of a Plasmid-Encoded Virulence Operon Expressing Escherichia coli Hemolysin

et al. 2002

View full text Add to dashboard Cite

show abstract

“…The YmoA protein is a temperature-dependent modulator of different virulence genes, and it has been suggested that it may have a role in DNA topology (5). In fact, we have recently reported that the hha mutation increases hemolysin expression through changes in the DNA topology (3). In this work, we describe a 220-bp DNA sequence within hlyC which modulates hly transcriptional expression possibly by its interaction with the Hha protein, either directly or through Hha interaction with some other protein(s).…”

mentioning

confidence: 99%

hlyM, a transcriptional silencer downstream of the promoter in the hly operon of Escherichia coli

et al. 1995

View full text Add to dashboard Cite

Transcription of the hly operon of transmissible plasmids in Escherichia coli is subject to a tight regulation which also involves various chromosomal genes, such as hha. We have identified a 200-bp region within the hlyC gene, designated hlyM, which modulates hemolysin expression. The deletion of hlyM increased the activity of hly::galK fusion 20-fold. hlyM does not contain any internal promoter, nor is it capable of acting in trans. Our data suggest that the chromosomal Hha protein interacts with hlyM in order to silence the hly promoter. In addition, hlyR, a positive activator of hemolysin expression, seems to suppress the modulatory effect dictated by the Hha protein on the hlyM region.Synthesis and secretion of hemolysin are determined by the hly operon located either on the chromosome or on conjugative plasmids (10). Transcription of the hly operon produces a major 4-kb hlyCA transcript and a minor 8-kb hlyCABD transcript (31). The two transcripts initiate at the same promoter, located upstream of the hlyC gene (12, 31). The minor transcript is thought to be produced by readthrough, or antitermination, at a Rho-independent transcriptional terminator located between hlyA and hlyB (15). Similar patterns of expression have been reported for the leukotoxins of Pasteurella (27) and Actinobacillus (26) species.In the case of the plasmid hly operons, a 600-bp sequence (hlyR) located 1.5 kb upstream of hlyC is known to increase hemolysin expression (29). The primary mechanism by which hlyR exerts its action has been proposed to be antitermination at the hlyA-hlyB transcriptional terminator (15,16).Hemolysin expression is a rather complex process in which chromosomal genes are involved as well. Three of them, tolC (30), hha (9, 21), and more recently sfrB (1), have been identified. The hha gene was identified during analysis of hemolysin expression in cells harboring the hemolytic recombinant plasmid pANN202-312, which contains the cluster hlyCABD from

show abstract

“…These proteins, which share an 82% amino acid identity, modulate the expression of virulence factor genes. The pleiotropic phenotypes exhibited by hha and ymoA mutants include altered plasmid supercoiling [11] and increased IS transposition [12,13]. Both of these properties, which are reminiscent of those of the E. coli hns mutants, suggested that Hha and YmoA are a distinct family of nucleoid associated proteins that modulate bacterial gene expression [12,13].…”

Section: Hha-like Proteins: a Distinctive Regulatory Element Of The Ementioning

confidence: 99%

“…Studies on the mechanism of action of the Hha protein are based on the Hha-mediated environmental down-regulation of the hlyCABD operon in E. coli, which encodes the toxin α-haemolysin [9,11]. Hha does not bind directly to specific DNA sequences of the hlyCABD operon.…”

Section: Hha-like Proteins: a Distinctive Regulatory Element Of The Ementioning

confidence: 99%

Bacterial Hha-like proteins facilitate incorporation of horizontally transferred DNA

Paytubi

García

Juárez³

2011

Open Life Sciences

View full text Add to dashboard Cite

Horizontal gene transfer (HGT), non-hereditary transfer of genetic material between organisms, accounts for a significant proportion of the genetic variability in bacteria. In Gram negative bacteria, the nucleoid-associated protein H-NS silences unwanted expression of recently acquired foreign DNA. This, in turn, facilitates integration of the incoming genes into the regulatory networks of the recipient cell. Bacteria belonging to the family Enterobacteriaceae express an additional protein, the Hha protein that, by binding to H-NS, potentiates silencing of HGT DNA. We provide here an overview of Hha-like proteins, including their structure and function, as well as their evolutionary relationship. We finally present available information suggesting that, by expressing Hha-like proteins, bacteria such as Escherichia coli facilitate HGT incorporation and hence, the impact of HGT in their genetic diversity.

show abstract

Escherichia coli hha mutants, DNA supercoiling and expression of the haemolysin genes from the recombinant plasmid pANN202‐312

Cited by 48 publications

References 31 publications

Temperature- and H-NS-Dependent Regulation of a Plasmid-Encoded Virulence Operon Expressing Escherichia coli Hemolysin

Temperature- and H-NS-Dependent Regulation of a Plasmid-Encoded Virulence Operon Expressing Escherichia coli Hemolysin

hlyM, a transcriptional silencer downstream of the promoter in the hly operon of Escherichia coli

Bacterial Hha-like proteins facilitate incorporation of horizontally transferred DNA

Contact Info

Product

Resources

About