Programmed -1 ribosomal frameshifting is a mechanism of gene expression, whereby specific signals within messenger RNAs direct a proportion of translating ribosomes to shift -1 nt and continue ...translating in the new reading frame. Such frameshifting normally occurs at a set ratio and is utilized in the expression of many viral genes and a number of cellular genes. An open question is whether proteins might function as trans-acting switches to turn frameshifting on or off in response to cellular conditions. Here we show that frameshifting in a model RNA virus, encephalomyocarditis virus, is trans-activated by viral protein 2A. As a result, the frameshifting efficiency increases from 0 to 70% (one of the highest known in a mammalian system) over the course of infection, temporally regulating the expression levels of the viral structural and enzymatic proteins.
Clostridium difficile infection (CDI) is a serious problem within the healthcare environment where the bacterium causes symptoms ranging from mild diarrhoea to life-threatening colitis. In addition ...to its principal virulence factors, Toxin A and Toxin B, some
C. difficile strains produce a binary toxin (CDT) composed of two sub-units namely CDTa and CDTb that are produced and secreted from the cell as two separate polypeptides. Once in the gut these fragments have the potential to combine to form a potent cytotoxin whose role in the pathogenesis of CDI is presently unclear. Here, we describe expression and purification methods for recombinant CDTa and CDTb produced in
Escherichia coli. We show that purified CDTa and CDTb can combine to form an active CDT which is cytotoxic to Vero cells. In addition, the purification processes described will allow milligram quantities of binary toxin fragments to be produced for further functional and structural studies.
Department of Medicine, Royal Free and University College Medical School, University College London, Royal Free Campus, Rowland Hill Street, London NW3 2PF, UK 1
Department of Hepatitis, National ...Institute for the Control of Pharmaceuticals and Biological Products, Temple of Heaven, Beijing, PR China 2
Author for correspondence: Tim Harrison. Fax +44 20 7433 2852. e-mail t.harrison{at}rfc.ucl.ac.uk
Isolates of hepatitis E virus (HEV) have recently been described from China that are distinct from Burmese, Mexican and US viruses and constitute a novel genotype (genotype 4). Here, the complete genomic sequence of a representative isolate of genotype 4 HEV, amplified directly from the stool of an acutely infected patient, is presented. Analysis of the entire sequence confirms our previous conclusion, based upon partial sequence data, that these Chinese isolates belong to a novel genotype. Typical of genetic variation in HEV, most nucleotide substitutions occur in the third base of the codon and do not affect the amino acid sequence. The genotype 4 virus is unusual in that a single nucleotide insertion in the ORF 3 region changes the initiation of ORF 3, and perhaps also ORF 2. The consequences of these changes are discussed.
Reviews "Mosaics of faith : floors of pagans, Jews, Samaritans, Christians, and Muslims," by Rina Talgam (Yad Ben-Zvi Press and Pennsylvania State University Press, 2014).
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