DNA Carries Genetic Information

Even though Miescher and many others following him suspected that nuclein or nucleic acid might play a key role in cell inheritance, others argued that their lack of chemical diversity compared to, say, proteins ruled out such a possibility. It was not until 1943 that the first direct evidence emerged for DNA as the bearer of genetic information. In that year, Oswald Avery, Colin MacLeod, and Maclyn McCarty, working at the Rockefeller Institute, discovered that DNA taken from a virulent (disease-causing) strain of the bacterium Streptococcus pneumonae permanently transformed a non-virulent (or inactive) form of the organism into a virulent form.
Avery and his colleagues concluded from these experiments that it was the DNA from the virulent strain which carried the genetic message for virulence and that it became permanently incorporated into the DNA of the recipient non-virulent cells. Although the scientific community was slow to adopt the idea that DNA was the carrier of genetic information, a subsequent experiment provided evidence that this was indeed the case. In 1952, Alfred Hershey and Martha Chase showed by means of radioactive isotope tracer experiments that when a bacterial virus (bacteriophage T2) infects its host cell (the bacterium Escherichia coli), it is the DNA of the T2 virus, and not its protein coat, which enters the host cell and provides the genetic information for replication of the virus.
From these very important early experiments, and a wealth of other corroborating evidence, it is now certain that DNA is the carrier of genetic information in all living cells.