(b) How is trp attenuation overridden in E. coli when tryptophan is scarce (缺乏的)? (5 points)

3. Consider two theoretical eukaryotic transposons, A and B.Each contains an intron. Each transposes to a new location in the yeast genome and then is examined for the presence of the intron. In the new locations, you find that A has no intron, but B does. What can you conclude about the mechanisms of transposition movement for A and B from these facts? (3 points)