Use the following information to answer the next few questions.
Poliovirus is a positive-sense RNA virus of the picornavirus group. At its 5' end, the RNA genome has a viral protein (VPg) instead of a 5' cap. This is followed by a nontranslated leader sequence, and then a single long protein coding region (~7000 nucleotides), followed by a poly-A tail. Observations were made that used radioactive amino acid analogues. Short-period use of the radioactive amino acids result in labelling of only very long proteins, while longer periods of labelling result in several different short polypeptides.
-What conclusion is most consistent with the results of the radioactive labelling experiment?
A)The host cell cannot translate viral protein with the amino acid analogues.
B)Host cell ribosomes only translate the viral code into short polypeptides.
C)The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones.
D)The RNA is translated into short polypeptides, which are subsequently assembled into large ones.
E)The large radioactive polypeptides are coded by the host, whereas the short ones are coded for by the virus.

Question

Quizplus · Accepted Answer

The observation that short-term radioactive amino acid labelling results in only very long proteins implies that the translation machinery is engaged in translating the long protein-coding region almost exclusively. The observation that longer labelling periods produce several different short polypeptides suggests that the long polypeptide is cleaved into smaller, distinct proteins. Therefore, the conclusion that best explains the results is that the RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones.

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