Final answer:
Phage-encoded proteins are coded for by phage DNA and are considered early proteins, which was shown through the Hershey and Chase experiments using isotopic labeling with 32P and 35S to demonstrate that DNA, not protein, is the genetic material transferred to host cells during phage infection.
Step-by-step explanation:
Phage-encoded proteins are coded for by phage DNA and can be classified as early proteins that are synthesized soon after infection. In the historical Hershey and Chase experiments, bacteria were infected with bacteriophages that had their DNA labeled with radioactive phosphorus (32P), while other batches had their protein coats labeled with radioactive sulfur (35S). This distinction allowed researchers to conclude that the genetic material of the phage is DNA, not protein, because after the infection process, the 32P label was found within the host bacteria cells, indicating that the DNA had entered the cells. The 35S labeled protein was found remaining outside the host cells in the supernatant, indicating that proteins did not enter the cells during infection. Thus, Hershey and Chase's findings solidified the understanding that DNA is the hereditary material responsible for carrying the information required to produce progeny phages, as the cells infected with 32p-labeled DNA produced labeled progeny phages, whereas those infected with 35S-labeled protein coats did not.