Avery, Mcleod & McCarty

Question 1

What did they do?

Answer 1

• Isolated DNA from the dead S-strain of bacteria split them into 2 test tube:
• Purified the DNA so that no protein was present and found that this extract would transform the non-virulent R-strain into the S-strain
• Next, they extracted deoxyribose nuclease enzyme from dog and rabbit blood and used it to digest DNA (removed it)
• Added R-strain, no S-strain occurred (no transformation)

Question 2

•The digested DNA would not…

Answer 2

transform the non-virulent R-strain into the S-strain - concluded DNA was the ‘transforming principle’

Question 3

What did they use?

Answer 3

• Cell-free extract of s cells
• From 75L or cell culture obtained 10-25 mg of “active factor”
• Proteases, RNases, DNases, etc