= Polyprotein
A <polyprotein> is a <polypeptide chain> that supplies several <protein> products through <proteolysis>. One translation product can therefore contain the sequences of multiple eventual products. This differs from a <protein complex> assembled by association of independently made chains.
The relationship can be tested by mapping product sequences back onto a precursor. In 1981, investigators determined the <poliovirus> <RNA> sequence and identified a long <open reading frame>. <Amino acid> sequence analysis mapped twelve viral <polypeptides> to cleavage products of the encoded <polyprotein>. Agreement between the sequence and the isolated products supported a common precursor, rather than merely grouping similar-sized bands together.<Primary structure, gene organization and polypeptide expression of poliovirus RNA by N. Kitamura and others>[Original Abstract: open reading frame and mapping of proteolytic products]{ref}
For an original accounting example, suppose a hypothetical precursor consists of consecutive regions of 200, 150 and 250 <amino acid residues>. Two cuts at the boundaries can yield three chains containing 600 residues altogether. Cleavage increases the number of molecules without synthesizing additional <amino acid residues>. Partial processing would also produce intermediates containing more than one of the regions.
The precursor and the final products need not have identical functions or lifetimes. An assay recognizing a sequence retained in several intermediates can detect more than one molecular species. Identifying a <polyprotein> thus requires following both its <protein primary structure> and its processing state.
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