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The size and location of the poly(A) tract in EMC virus RNA
Abstract:
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.
Insights
Encephalomyocarditis virus RNA contains poly(A) tracts of varying lengths, primarily 16-18 nucleotides, located at the 3' terminus. A minimum of 13 adenine residues are essential for EMC virus RNA infectivity.
Area of Science:
- Virology
- Molecular Biology
- RNA Biochemistry
Background:
- Encephalomyocarditis (EMC) virus is a cardiovirus with a polyadenylated RNA genome.
- Polyadenylation is a crucial post-transcriptional modification in eukaryotic mRNA, affecting stability and translation.
- Understanding the structure and function of poly(A) tails in viral RNA is vital for comprehending viral replication and pathogenesis.
Purpose of the Study:
- To characterize the size and location of the poly(A) tail in Encephalomyocarditis (EMC) virus RNA.
- To compare the poly(A) tail characteristics of EMC virus with other picornaviruses.
- To determine the minimum poly(A) tail length required for EMC virus RNA infectivity.
Main Methods:
- RNA isolation and selection using oligo(dT)-cellulose affinity chromatography.
- RNase digestion (pancreatic and T1) to analyze poly(A) tract resistance and composition.
- Polyacrylamide gel electrophoresis to determine poly(A) tract size using molecular weight markers.
- Compositional analysis of terminal residues to confirm 3'-terminus and adenine content.
Main Results:
- EMC virus RNA possesses poly(A) tracts with an average size of approximately 14-15 nucleotides, with heterogeneity observed between 12-45 nucleotides (majority 16-18).
- Compositional analysis confirmed the poly(A) tract is located at the 3'-terminus of the EMC virus genome.
- A poly(A) tract of at least 13 adenine residues is necessary for the full infectivity of EMC virus RNA.
Conclusions:
- The poly(A) tail of EMC virus RNA is relatively short compared to some other picornaviruses, with sizes potentially overestimated in previous studies.
- The size heterogeneity of the poly(A) tract supports its terminal location.
- The findings provide insights into the minimal requirements for picornavirus RNA infectivity and comparative viral genomics.