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.
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).