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A protein-dependent riboswitch activates ribosomal frameshifting in cardioviruses.

Programmed -1 ribosomal frameshifting (PRF) is a translational control mechanism used by RNA viruses to regulate the relative abundance of proteins encoded in different reading frames. Cardioviruses exhibit the highest known PRF efficiency, with ∼85% of ribosomes shifting into the -1 frame. This unusual event requires an interaction between the viral 2A protein and a stimulatory element in the RNA genome, but the basis for protein dependence is unclear. To address this, here we investigate the structure and dynamics of the PRF signal in Theiler's murine encephalitis virus (TMEV). By combining X-ray crystallography, small-angle X-ray scattering (SAXS), and single-molecule fluorescence resonance energy transfer (smFRET), we show that 2A binding switches the RNA from a stem-loop conformation into a pseudoknot, and we demonstrate that pseudoknot formation is essential for efficient PRF in vitro and in cells. Together, these findings illustrate how the cardiovirus PRF element behaves as a protein-dependent riboswitch, defining the molecular mechanism by which frameshifting is conditionally activated.

Frameshifting, Ribosomal

Sikhote-Alin virus, a new member of the cardiovirus group (Picornaviridae) isolated from Ixodes persulcatus ticks in Primorie Region.

A virus, designated Sikhote-Alin, was isolated in 1970 from Ixodes persulcatus ticks collected from a wild boar in the Primorie region (U.S.S.R.) Sikhote-Alin virus showed no haemagglutinating activity and no antigenic relationships with arboviruses of 12 antigenic groups, 17 ungrouped tick-borne arboviruses, porcine enteroviruses and coxsackie A (types 1-18) viruses. An one-way antigenic relationship was demonstrated by complement fixation with cardioviruses (Mengo and Columbia-SK strains). The virus contains RNA, is resistant to lipid solvents, highly thermostable in the presence of 1 M MgCl2 and its size is over 20 nm but less than 25 nm. All these properties make it possible to consider it as a new member of the cardiovirus group (genus Enterovirus; Picornaviridae).

Animal Population Groups

Sequence and location of the poly C tract in aphtho- and cardiovirus RNA.

The poly C tract in the RNA of the aphtho- and cardio viruses has been examined in several isolates of foot-and-mouth disease virus (FMDV) and encephalomyocarditis (EMC) virus. The length of the tract is variable, containing 100 to 170 bases in the FMDV isolates and 80 to 250 bases in the EMC virus isolates. Each poly C tract contains c. 10% A and U residues, located at the 5' end, i.e. most of the tract is a continuous run of C residues. The position of the tract on the genome was the same in each of the FMDV isolates, about 400 bases from the 5' end, whereas in the EMC virus isolates it was about 150 bases from the 5' end.

Animals

The importance of picornavirus infections in respiratory disease of man and other mammals.

Picornaviruses may be divided, by physicochemical properties, into enteroviruses, cardioviruses, caliciviruses, rhinoviruses and foot-and-mouth diseases viruses. Although the respiratory tract may be the primary site of entry and multiplication for enteroviruses, cardioviruses and FMD viruses, few agents in these groups cause respiratory disease. A notable exception is coxsackievirus A21 which is an important cause of upper respiratory tract diseases in military recruits. The picornaviruses which most frequently cause respiratory illness are rhinoviruses and caliciviruses. There are over one hundred rhinovirus serotypes which infect man and they have been isolated from up to 50 percent of cases of mild respiratory illness, from 1-2 percent of healthy adults and from 5-10 percent of healthy children. About 10 percent of rhinovirus infections in adults are symptomless. The two bovine serotypes of rhinovirus and the two equine serotypes frequently infect cattle and horses respectively but seldom cause disease. Numerous calicivirus serotypes have been found in 17 percent of cats with respiratory disease and in 19 percent of clinically normal cats. However, experimental inoculation with caliciviruses has confirmed their causative role in respiratory disease of cats. The high rate of virus isolation from normal cats is probably due to their ability to carry virus in an infectious form for up to two years after initial infection and illness.

Adult

The size and location of the poly(A) tract in EMC virus RNA.

Encephalomyocarditis (EMC) virus RNA, selected by its affinity for oligo(dT)-cellulose, contains poly(A) of size : (i) about 14 nucleotide residues long, based on the percentage of radioactivity in the RNA resistant to digestion by a mixture of pancreatic and T1 RNases; (ii) about 15 residues long, as measured by the ratio of the amount of terminal adenosine to internal adenylic acid in isolated poly(A); and (III) in the range 12 to 45 residues, the majority of tracts being about 16 to 18 residues long, based upon electrophoretic mobility on polyacrylamide gels using poly(A) molecules of known size as mol. wt. markers. The poly(A) appears to be located at the 3'-terminus of the virus genome since the tract, liberated by digestion with a mixture of pancreatic and T1 RNases, was shown by compositional analysis to contain a non-phosphorylated 3'-terminus and only adenine residues. The size heterogeneity in the poly(A) tracts revealed by gel electrophoresis is also consistent with a terminal location. Comparison of our data for EMC virus with published data for other picornaviruses suggests that the sizes of poly(A) tracts in polio- and Mengovirus RNA have been overestimated; poly(A) tracts in cardioviruses appear to be smaller than those in poliovirus; the minimum size of poly(A) required for full infectivity of picornavirus RNA has also been overestimated; a tract of at least 13 adenine residues long is required for full infectivity of EMC virus RNA.

Base Sequence

Antiviral effect of 3-[bis-(2-hydroxyethyl)-amino]-acetophenone-[4,5-diphenyl-oxyazolyl-(2)]hydrazone (IMET 98/69) in mice.

The potential in vivo antiviral activity of 3-[bis-(2-hydroxyethyl)-amino]-acetophenone-[4,5-diphenyl-oxazolyl-(2)]-hydrazone (IMET 98/69) was evaluated on model infections in mice. Animals treated subcutaneously (s.c.) with 1 mmole of the drug per kg body weight once daily for five days were significantly protected against a lethal infection with cardioviruses, Semliki forest virus and vaccinia virus. In influenza A and B virus models no antiviral activity was observed either after s.c. or oral treatment.

Administration, Oral