Concept explainers
Not all proteins are made from the RNA genome of bacteriophage MS2 in the same amounts. Can you explain why? One of the proteins functions very much like a repressor, but it functions at the translational level. Which protein is it and how does it function?
The RNA bacteriophage are very small, around 25 nm in diameter with icosahedral virion structure. For example, MS2 (having positive strand RNA) virus has a small genome, which encodes only four types of proteins. These are 1) Mutation proteins, which are present as a single copy in a mature virion, 2) coat protein, 3) lysis protein and 4) subunit of RNA replicase (it is the enzyme, which replicates the viral RNA). RNA replicase protein consists of one virus encoded polypeptide and many peptides of the host.
Explanation of Solution
The RNA of phage MS2 is folded in a complicated way, thereby, leading to formation of an extensive secondary structure. The translation at coat protein site on m-RNA starts very early upon viral infection, as it is most accessible to translation machinery among the four AUG translation sites. The m-RNA replicase enzyme also translate early. Since coat proteins translate early, they start increasing in number in number within the cell. Coat proteins start binding to RNA at AUG region, which is the initiation site for replicase protein and shit down the production of replicase. Therefore, coat protein also acts like a repressor protein. Also due to extensive folding of RNA limited copies maturation protein is produced even though it is present at 5’ end. Thus translation regulation occurs due to the folding of RNA, thereby, producing limited proteins for viral assemble. Coat protein, however is required in large quantity, therefore it is majorly produced.
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Chapter 10 Solutions
Brock Biology of Microorganisms (15th Edition)
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