What do the enzymes topoisomerase I and topoisomerase II have in common?
A) They both have nuclease activity. B) They both create double-strand DNA breaks. C) They both require ATP hydrolysis for their function. D) They both can create winding (tension) in an initially relaxed DNA molecule. E) All of the above.
You have found a strain of Escherichia coli that has an unusually short doubling time of only 15 minutes, despite the fact that its complete DNA replication should take almost 35 minutes. You also find that there is only one replication origin on its chromosome from which two forks originate, just like the normal process described for E. coli. However, you discover that the origin of replication in this strain has a significantly shorter "refractory period," resulting in the reactivation of the origin before the previous round of replication is over. Based on this model, if you examine the chromosomes of this strain (under conditions of fast growth), how many replication forks would you expect to observe per chromosome on average?
A) Two, just like the wild-type strain B) Four C) Six D) Eight E) Ten
The Dam methylase is responsible for methylating the adenine base in GATC sequences in Escherichia coli. Imagine two
A) Both of the strains B) Neither of them C) Only the first strain D) Only the second strain E) coli strains, one without any active Dam methylase, and the other with a hyperactive version of the enzyme that operates faster than the wild-type enzyme. Which of these strains would you expect to show a "mutator" phenotype?