What was the prevailing belief about the genetic material before the work of Avery, MacLeod and McCarty?

Step-by-step solution

Prior to the work of Oswald Avery, Colin MacLeod and Maclyn McCarty (1933-44), the genetic material was thought to be a protein . They worked to determine the biochemical nature of ‘transforming principle’ in Griffith's experiment. They purified biochemicals (proteins, DNA, RNA, etc.) from the heat-killed S cells to see which ones could transform live R cells into S cells. They discovered that DNA alone from S bacteria caused R bacteria to become transformed. They also discovered that protein-digesting enzymes (pro