Evidence of ambiguous processing and selective degradation in the noncapsid proteins of rhinovirus 1A.

Pulse-chase kinetics and extensive pactamycin mapping studies show that the translation of rhinovirus 1A proceeds in the order: initiate-P1-S-P2-terminate, where P1 is the precursor to the capsid proteins, S is a stable primary gene product, and P2 is the precursor to a family of noncapsid products. Initial examination of the molar stoichiometry of the families of rhinoviral proteins in infected cells suggested that both the P1 and P2 regions were translated more frequently than the S region. However, we show that this apparent asymmetry in translation is an artifact arising from two phenomena: (i) ambiguous cleavage sites which result in two alternative products from the S region, having apparent molecular weights of 47,000 and 38,000, and (ii) several fates for the P2 precursors, including degradation of 35 to 45% of the P2 family to small unidentifiable products. Another artifact, a time-dependent shift in the pactamycin mapping position of polypeptide r-39, was traced to a selective inhibition of the rate of cleavage of its precursor (peak 76). The processing rate of the capsid precursor (peak 92) was not retarded by pactamycin.