Poliovirus is a positive-stranded RNA virus. Thus, the genome enclosed within the viral particle can be used as messenger RNA and immediately translated by the host cell. On entry, the virus hijacks the cell's translation machinery, causing inhibition of cellular protein synthesis in favor of virus-specific protein production. Unlike the host cell's mRNAs, the 5' end of poliovirus RNA is extremely long—over 700 nucleotides—and highly structured. This region of the viral genome is called internal ribosome entry site (IRES). This region consists of many secondary structures and 3 or 4 domains. The most important domain of IRES is domain 3 that (translation initiation part). Domain 3 is a self folding RNA element that contains conserved structural motifs in various stable stem loops linked by two four-way junctions. As IRES consists of many domains these domains also consist of many loops that contribute the modified translation without 5’ end cap by hijacking cell ribosome unlike dogmatic translation started not from the first step but started from the latter steps. The interaction loop of domain 3 is GNRA tetraloop. The residues of adenosines A180 and A181 in the GUAA tetraloop forms hydrogen bonds via non canonical base pairing interactions with the base pairs of the receptors C230/G242 and G231/C241, respectively. Genetic mutations in this region prevent viral protein production. The first IRES to be discovered was found in poliovirus RNA.