Effect of delay mismatch in Pyragas feedback control.

Pyragas time-delayed feedback is a control scheme designed to stabilize unstable periodic orbits, which occur naturally in many nonlinear dynamical systems. It has been successfully implemented in a number of applications, including lasers and chemical systems. The control scheme targets a specific unstable periodic orbit by adding a feedback term with a delay chosen as the period of the unstable periodic orbit. However, in an experimental or industrial environment, obtaining the exact period or setting the delay equal to the exact period of the target periodic orbit may be difficult. This could be due to a number of factors, such as incomplete information on the system or the delay being set by inaccurate equipment. In this paper, we evaluate the effect of Pyragas control on the prototypical generic subcritical Hopf normal form when the delay is close to but not equal to the period of the target periodic orbit. Specifically, we consider two cases: first, a constant, and second, a linear approximation of the period. We compare these two cases to the case where the delay is set exactly to the target period, which serves as the benchmark case. For this comparison, we construct bifurcation diagrams and determine any regions where a stable periodic orbit close to the target is stabilized by the control scheme. In this way, we find that at least a linear approximation of the period is required for successful stabilization by Pyragas control.

EHV-1 gene63 is not essential for in vivo replication in horses and mice, nor does it affect reactivation in the horse: short communication.

The aim of this study was to investigate the role of immediate early gene (gene63) in the pathogenesis of equine herpesvirus 1 (EHV-1) acute and latent infections in equine and murine models. EHV-1 gene63 mutant virus (g63mut) along with EHV-1 (Ab4) was used for intracerebral and intranasal infection of 3 and 17-day-old mice. Both viruses were recovered at the same frequency from tissues after infection. Two Welsh ponies were infected via the intranasal route with each of the viruses. Acute infection was monitored by virus isolation from nasal swabs and peripheral blood leukocytes. Six weeks post infection, peripheral blood leukocytes were taken from ponies and in vitro reactivation was positive for both viruses. At autopsy, both viruses were isolated by co-cultivation from bronchial and submandibular lymph nodes. These findings indicate that the mutation of EHV-1 gene63 does not play a role in the establishment and reactivation from latency.

The equid herpesvirus-1 gene 63 is expressed as a leaky late (gamma 1) transcript and is nonessential for replication in vitro.

The regulation of Equid herpesvirus-1 (EHV-1) gene 63 was investigated using molecular expression studies and its role in viral growth was identified by constructing a gene 63 mutant virus. Metabolic inhibitors were used to show that EHV-1 gene 63 is expressed as a leaky-late (gamma 1) transcript. Transient transfections and subsequent chloramphenicol acetyltransferase (CAT) reporter assays showed that gene 63 was transactivated by EHV-1 gene 64 (immediate early) protein. An EHV-1 gene 63 mutant virus, where the LacZ gene was inserted into the mutated gene 63 open reading frame, showed that gene 63 protein was not essential for efficient EHV-1 growth in tissue culture. These findings indicate that the animal alpha herpesviruses may have evolved different pathways leading to replication.

Equid herpesviruses 1 and 4 encode functional homologs of the herpes simplex virus type 1 virion transactivator protein, VP16.

The herpes simplex virus type 1 (HSV-1) tegument protein VP16 is a potent transcriptional inducer of immediate-early gene expression, comprising an N-terminal domain involved in binding DNA linked to an acidic transactivating C-terminal domain. The gene encoding the counterpart of this protein in equid herpesvirus 4 (EHV-4) was sequenced. Comparisons with VP16 and the homologous proteins of equine herpesvirus 1 (EHV-1) and varicella-zoster virus (VZV) showed that a region in the N-terminal domain involved in formation of a complex with cellular proteins is partially conserved in all four proteins. In contrast, the C-terminal regions of the EHV proteins, like that of VZV, are not particularly acidic and are not significantly conserved with respect to the C-terminal region of VP16. Nevertheless, transient expression experiments indicated that the EHV-1 and EHV-4 proteins are able to transactivate HSV-1 and EHV-1 immediate-early promoters in a dose-dependent manner, which suggests that this activity is not dependent on an acidic C-terminal domain.

Cross-hybridization of equid herpesvirus-2 (EHV-2) and herpes simplex virus-1 (HSV-1) genes to equid herpesvirus-1 (EHV-1).

In contrast to previous findings, the Ab4 isolate of equid herpesvirus-1 (EHV-1) was shown to share homology with the G9 isolate of equid herpesvirus-2 (EHV-2). Using Southern blotting and stringent hybridization conditions, a significant proportion of this cross-hybridization was identified by the immediate-early gene-3 (IE-3) probe from herpes simplex virus-1 (HSV-1). The HSV-1 UL48 gene probe (encoding the IE gene transactivating protein VmW65, which is also known as alpha-TIF or VP16) was used to identify and isolate its counterpart in EHV-1. The relevance of shared homology to transactivation is being investigated.

Substrate specificity and energetics of antiseptic and disinfectant resistance in Staphylococcus aureus.

Clinical isolates of Staphylococcus aureus carry various antiseptic and disinfectant resistance determinants (qac genes) on a variety of plasmids. The biochemistry and specificity of these resistance genes in S. aureus is the subject of this report. The qac genes were separated into two families on the basis of resistance profiles and DNA homology. Isotopic and fluorimetric assays demonstrated that the qac genes encode efflux systems that rely on proton motive force.

Identification and control of the cis-acting elements of the immediate early gene of equid herpesvirus type 1.

Consensus cis-acting DNA sequences upstream of the immediate early (IE) gene of equid herpesvirus type 1 (EHV-1, strain Ab4) were identified. One copy of the conserved motif TAATGARATTC, which is the binding site for the host cellular factor Oct-1 and herpes simplex virus type 1 (HSV-1) virion protein, VmW65, complex, was identified at positions -630 to -620. Using transient transfections and chloramphenicol acetyltransferase assays the IE promoter of EHV-1 was shown to be trans-activated by VmW65 within the region -685 to +73. Ultraviolet light-inactivated EHV-1 was able to stimulate the expression of the IE gene of EHV-1 as well as HSV-1, indicating that EHV-1 possesses a protein equivalent to VmW65. The ubiquitous equid herpesvirus type 2 (EHV-2), which is not known to be a primary pathogen, was also able to trans-activate the EHV-1 and HSV-1 IE genes. Further work is being performed in order to identify the nature of the EHV-1 and EHV-2 trans-activating proteins.

Nucleotide sequence of the ethidium efflux gene from Escherichia coli.

The nucleotide sequence of the gene specifying the ethidium efflux system of Escherichia coli has been determined. The translated open reading frame has identified a membrane-bound polypeptide of 110 amino acids (11,960 Da) which shares 42% identity with a staphylococcal protein specifying resistance to ethidium.

Cloning of the ethidium efflux gene from Escherichia coli.

The gene specifying the ethidium efflux system of Escherichia coli has been cloned on a 3.2 kbp HindIII fragment and located on a 1.2 kbp fragment within this. Cross-resistance studies indicate that the system has a broad specificity for monovalent cations and the gene shows no hybridisation with similar genes found in Staphylococci.

Physical and biochemical characterization of the qacA gene encoding antiseptic and disinfectant resistance in Staphylococcus aureus.

We have previously cloned a 3.5 kb fragment from the Staphylococcus aureus multiresistance plasmid pSK1 which carries the qacA determinant responsible for linked resistance to acriflavine (Acr), ethidium bromide (Ebr), quaternary ammonium compounds (Qar), propamidine isethionate (Pir), and diamidinodiphenylamine dihydrochloride (Ddr). This report presents a biochemical and physical analysis of qacA and shows the widespread carriage of this gene on S. aureus resistance plasmids. Tn5 insertion mutagenesis defined the extent of qacA to within 2.40 kb of pSK1 DNA. Examination of the expression of insertion and deletion mutants of the cloned qacA sequences in both maxicells and minicells led to the association of a 50 kDa protein, designated QacA, with the AcrEbrQarPirDdr phenotype. Based on fluorimetric and isotopic assays used to determine the extent of accumulation of ethidium bromide by S. aureus strains harbouring pSK1, we propose that the basis of AcrEbrQarPirDdr in S. aureus is a qacA-mediated efflux system.