Basis of genetics (Avery, McLeod)
Experiments using pneumococcus.
Pneumococcus exists in two forms:
R-form ("rough"), lacks capsule that protects it from immune systems, non-pathogenic.
S-form ("smooth"), contains capsule that prevents immune system from destroying it, consequently pathogenic
(1) Bacteria that were infected by non-pathogenic R form were cultured.
(2) Bacteria infected with the S-form were heat-treated (killed). The solution was divided into 3 aliquots. Each was treated with a different enzyme:
a. protease (e.g., trypsin)
(3) The culture of live, R-form (non-pathogenic) infected bacteria was divided into three aliquots, with one added to each enzyme-treated aliquot (step 2)
(4) Protea and RNAase treated solutions were able to transform the R-infected cells to the S-form. The DNase-treated cells were not capable of changing the R to S.
Conclusion: the transformation from R to S was DNA mediated.