THE PROCESSING MAP OF POLIOVIRAL POLYPROTEIN

The map of rhinovirus 1A raises the question as to which of the alternative cleavage pathways have functional significance and which are mere accidents. Evidence that the alternative cleavage modes are not mere pecularities of rhinovirus 1A, but are preserved in detail through evolution and therefore probably have functional significance,comes from comparative studies on the processing of polioviral protein. 

Pigure 7. Proposed relationships among the major polypeptides produced in poliovirus-infected cells. The values enclosed in parentheses to the right of each polypeptide name refer to the apparent molecular weight of that polypeptide in the Mahoney strain. Not all polioviams strains produce detectable amounts of polypeptides Jc, 

At 210 minutes post-infection the cells were pulsed 10 minutes with 55s-methionine. The label was chased by-adding excess unlabeled methionine and cells were lysed at the indicated chase periods and electrophonesed on an SDS-polyacrylamide slab gel. 

7c if the amount of 6b is large so is the amount of 6a (not shown). All strains of poliovirus also produce a protein (MW 48f000) similar in size to that of rhinoviral protein 47 Tryptic analysis of Mahoney viral polypeptides has confirmed that 5t contains the sequences of X so does which is thus homologous to rhinoviral protein 60b. We have also confirmed that protein 2 contains the sequences of 4, 7c and 6a. 

The data reviewed here are still compatible with the single initiation site-single termination site model for picornaviral translation. It is evident that the S-protein region of the polioviral polyprotein can be expressed in forms other than X, i.e., also to form 5 and and that the P2 proteins are cleaved to products not previously accounted for. Hence it is clear that until these facts are taken into accoimt, apparent inequalities in family stoichiometry represent inadequate evidence for drawing conclusions about the nimaber of translational initiation or termination sites operating in picornaviral RNA. 

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