Poliovirus is an RNA virus of the picornavirus group, which uses its RNA as mRNA. 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 labeling of only very long proteins, while longer periods of labeling result in several different short polypeptides. What conclusion is most consistent with the results of the radioactive labeling experiment?
A) Host cell ribosomes only translate the viral code into short polypeptides.
B) The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones.
C) The RNA is translated into short polypeptides, which are subsequently assembled into large ones.
D) The large radioactive polypeptides are coded by the host, whereas the short ones are coded for by the virus.

Question

Quizplus · Accepted Answer

The presence of a single long protein-coding region followed by a poly-A tail suggests that the RNA is translated into a single long polypeptide. The observation that short periods of radioactive labeling result in labeling of only very long proteins suggests that the long polypeptide is the primary product. However, longer periods of labeling result in several different short polypeptides, indicating that the long polypeptide is then cleaved into shorter ones, as in option B. Option A is incorrect because the presence of both long and short polypeptides suggests that host cell ribosomes are not limiting translation to only short polypeptides. Option C is incorrect because it suggests that short polypeptides are being assembled into large ones, which is not supported by the observations. Option D is not supported by any evidence and is therefore incorrect.

Poliovirus Is an RNA Virus of the Picornavirus Group, Which