In silico structure analysis of alphaviral RNA genomes shows diversity in the evasion of IFIT1-mediated innate immunity

The IFIT (interferon-induced proteins with tetratricopeptide repeats) family constitutes a major arm of the antiviral functionof type I interferon (IFN). Human IFIT1, the earliest discovered member of this family, inhibits several viruses of positivestrand RNA genome. IFIT1 specifically recognizes single-stranded RNA with canonical 7-methylguanylate cap at the 50 end(Cap0), and inhibits their translation by competing with eIF4E (eukaryotic initiation factor 4E), an essential factor for 50Caprecognition. Recently, a novel viral mechanism of IFIT1 suppression was reported, in which an RNA hairpin in the 50untranslated region (50UTR) of the viral genome prevented recognition by IFIT1 and enhanced virus growth. Here, I haveanalyzed the in silico predicted structures in the 50UTR of the genomes of the Alphaviruses, a large group of envelopedRNA virus with positive-sense single-stranded genome. The results uncovered a large ensemble of RNA secondarystructures of diverse size and shape in the different viruses, which showed little correspondence to the phylogeny of theviruses. Unexpectedly, the 50UTR of several viral genomes in this family did not fold into any structure, suggesting eithertheir extreme sensitivity to IFIT1 or the existence of alternative viral mechanisms of subverting IFIT1 function.

When proteome meets genome: the alpha helix and the beta strand of proteins are eschewed by mRNA splice junctions and may define the minimal indivisible modules of protein architecture.

The significance of the intron-exon structure of genes is a mystery. As eukaryotic proteins are made up of modular functional domains, each exon was suspected to encode some form of module; however, the definition of a module remained vague. Comparison of pre-mRNA splice junctions with the three-dimensional architecture of its protein product from different eukaryotes revealed that the junctions were far less likely to occur inside the alpha-helices and beta-strands of proteins than within the more flexible linker regions ('turns' and 'loops') connecting them. The splice junctions were equally distributed in the different types of linkers and throughout the linker sequence, although a slight preference for the central region of the linker was observed. The avoidance of the alpha-helix and the beta-strand by splice junctions suggests the existence of a selection pressure against their disruption, perhaps underscoring the investment made by nature in building these intricate secondary structures. A corollary is that the helix and the strand are the smallest integral architectural units of a protein and represent the minimal modules in the evolution of protein structure. These results should find use in comparative genomics, designing of cloning strategies, and in the mutual verification of genome sequences with protein structures.