Why were proteins favoured over DNA as the genetic material before 1940? - University Genetics Past EXAM Question (May/02/2009 )

Why were proteins generally favoured over DNA as the genetic material before 1940?

You have to know a little bit about the history of DNA research.
"DNA's role in heredity was confirmed in 1952, when Alfred Hershey and Martha Chase in the Hershey-Chase experiment showed that DNA is the genetic material of the T2 phage"
You can find your answer here http://en.wikipedia.org/wiki/DNA#History_of_DNA_research

20 AAs vs. ATCG, what would you think?