Avery transformation experiment

Biochemical assay for transformation

    Oswald Avery & co-workers (1944) investigated the biochemical nature of Griffth's 'transforming principle'. He combined living R bacteria with heat-killed S filtrate, and subjected the mixture to enzyme treatments that successively destroyed first protein, then RNA, then DNA . Only the final DNAse treatment destroys the capacity of S to transform R. This indicates that the transforming substance is DNA.

    (1) The first experiment on the far right is described as a control: what does it control for?
    (2) What is an "Assay?" What is Avery's biological "Assay for Transformation"? How does it relate to the presence of R and / or S cells in the cultures on the third line above? How does this assay differ from Griffith's?
    (3) Suppose the first treatment was with DNAse, followed by RNAse, finally by protease. What results would you expect? What would they prove? Why did Avery do the experiments in the order he did?

All figure & text material ©2016 by Steven M. Carr