Chapter 9, Problem 14P

A plasmid vector pBS281 is cleaved by the enzyme BamHI (5′ G^GATCC 3′), which recognizes only one site in the DNA molecule. Human DNA is digested with the enzyme MboI (5′ ^GATC 3′), which recognizes many sites in human DNA. These two digested DNAs are now ligated together. Consider only those molecules in which the pBS281 DNA has been joined with a fragment of human DNA. Answer the following questions concerning the junction between the two different kinds of DNA.

a.	What proportion of the junctions between pBS281 and all possible human DNA fragments can be cleaved with MboI?
b.	What proportion of the junctions between pBS281 and all possible human DNA fragments can be cleaved with BamHI?
c.	What proportion of the junctions between pBS281 and all possible human DNA fragments can be cleaved with XorII (5′ C^GATCG 3′)?
d.	What proportion of the junctions between pBS281 and all possible human DNA fragments can be cleaved with BstYI (5′ R^GATCY 3′)? (R and Y stand for purine and pyrimidine, respectively.)
e.	What proportion of all possible junctions that can be cleaved with BamHI will result from cases in which the cleavage site in human DNA was not a BamHI site in the human chromosome?