A. Does the protein or RNA moiety act as the catalyst in this raMutant A S-UAAAC

Question

A. Does the protein or RNA moiety act as the catalyst in this raMutant A S-UAAACGAG- tion? Explain which reactions helped you make your conclusion. B. Propose the function of spermidine in the last two reactions. Mutant B 5-UAAAGCAG-3 GUUUGCUC Mutant C 5.UAAACGAG-3' Question 15. The genome of the bacteriophage QB consists of about 4000 nucleotides of single-stranded RNA. Inside the E. colihost, replication of this genome requires a RNA-dependentIn vitro replication efficiency (relative to wild type) RNA polymerase made up of phage and bacterial proteins. Inter- wild type: 100% estingly, the replicase binds to a region in the center of the RNA genome, yet must start copying the 3' end of the RNA template to produce anew strand of RNA in the 5' to 3' direction. Research- ers hypothesized that the presence of a predicted pseudoknot in the QB genome allowed the replicase to gain access to the 3'end of the RNA. To test their hypothesis, they measured the replication A. Predict why the replication efficiency so low in Mutant A. efficiency in vitro using wild-type replicase and different ver- sions of the QB RNA containing mutations in a region key to the B. Predict why the replication efficiency is restored to almost predicted pseudoknot formation. They specifßically GUUUGCUC Mutant A: 1.6% Mutant B: 0.6% Mutant C: 42% half of wild-type levels in Mutant C? an eight-nucleotide region from the center of the RNA that was complementary to the 3 -terminal hairpin. The wild-type and the mutant sequences and replication data are given below C. Do you think the results support or refute the hypothesis that presence of a pseudoknot affects replication? Wild type 5'-UAAAGCAG-3 Data adapted from Klovins and van Duin (1999. J. Mol. Biol 294: 875-884.) GUUUCGUC

Explanation / Answer

Bacteriophages of the Leviviridae family are small RNA viruses with linear, positive-sense, single-stranded RNA genomes that encode only four proteins. All phages of this family require bacterial pili to attach to and infect cells.

Leviviridaephages utilizing F-pili for this purpose have been extensively studied. RNA phages specific for conjugative plasmid-encoded pili other than that of plasmid F have been isolated

A.Q showed adaptation to growth at an inhibitory temperature. mutations that do not alter the amino acid sequence for adaptation of organisms to novel environmental conditionsthermal adaptation of Q, mutations that did not alter the amino acid sequence contributed to increases in fitness of the phage. Temperature is one of the environmental factors that affect the fitness of living organisms

The genome sequence of phage shows that it is clearly related to other conjugative pili-specific leviviruses but has an atypical location of the lysis gene. It provides a better view on the remarkable diversification of the plasmid-specific RNA phages.

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