The DNA of bacteriophage l is a linear double-stranded molecule that has complementary single-stranded ends. These molecules can form closed circular molecules when two âcohesiveâ ends on the same molecule join, and they can form linear dimers, trimers, or longer molecules when sites on different molecules are joined.
a) What conditions should be chosen to ensure that l phage DNA molecules form closed circular monomers, as opposed to dimers, trimers, etc?
b) Under certain, l phage DNA molecules are infective. When a very low concentration of l phage DNA is incubated with DNA polymerase I and the four deoxyribonucleoside triphosphates, the infectious activity of l phage DNA is destroyed. Brief treatment of l phage DNA with bacterial exonuclease III, an enzyme that removes 5â-mononucleotides from the 3â-ends of double-stranded DNA molecules, also destroys infectivity, but subsequent treatment of the DNA with DNA polymerase and nucleotide substrates can restore infectivity. What does this tell you about the structure of the cohesive ends of the DNA? Explain the effects of the two enzymes.
The DNA of bacteriophage l is a linear double-stranded molecule that has complementary single-stranded ends. These molecules can form closed circular molecules when two âcohesiveâ ends on the same molecule join, and they can form linear dimers, trimers, or longer molecules when sites on different molecules are joined.
a) What conditions should be chosen to ensure that l phage DNA molecules form closed circular monomers, as opposed to dimers, trimers, etc?
b) Under certain, l phage DNA molecules are infective. When a very low concentration of l phage DNA is incubated with DNA polymerase I and the four deoxyribonucleoside triphosphates, the infectious activity of l phage DNA is destroyed. Brief treatment of l phage DNA with bacterial exonuclease III, an enzyme that removes 5â-mononucleotides from the 3â-ends of double-stranded DNA molecules, also destroys infectivity, but subsequent treatment of the DNA with DNA polymerase and nucleotide substrates can restore infectivity. What does this tell you about the structure of the cohesive ends of the DNA? Explain the effects of the two enzymes.
