Autocatalytic processing of the wild-type and mutant BYV polyproteins upon translation in the wheat germ extracts. Mock, translation with no added mRNA (negative control); BMV, translation of Brome mosaic virus RNA (positive control); Parental, translation of RNA that encodes a wild-type L-Pro; A13 to A27, translation of RNAs that harbor corresponding mutant variants of L-Pro. The positions and molecular masses of translation products of BMV RNAs 2, 3, and 4 are shown at the left. The arrowheads between the two autoradiograms indicate positions of the nonprocessed polyprotein and processed L-Pro.