Final answer:
The Hershey-Chase experiment found that DNA was the infectious agent responsible for hereditary information in bacteriophages, not protein.
Step-by-step explanation:
The infectious agent found to be in the Hershey-Chase experiment was none other than DNA. The experiment conducted by Alfred Hershey and Martha Chase in 1952 was pivotal in confirming that DNA is the genetic material responsible for hereditary information in phages (viruses that infect bacteria). They labeled the DNA of bacteriophages with radioactive phosphorus (32P), knowing that phosphorus is a component of DNA but not protein, and the proteins with radioactive sulfur (35S). After allowing the phages to infect bacteria and then separating the phage protein coats from the bacteria, only the 32P, the marker for DNA, was found inside the bacterial cells, proving that DNA was the substance transferred from the viruses to the bacteria during infection. This provided strong evidence against protein being the hereditary material and supported the idea that DNA carries genetic information.