Remember that earlier experiment with capping and ribosome binding? The following questions asks you to integrate information from multiple sources and not just this lesson. In a similar experiment, a student synthesized mRNAs such that 32P-GTP was incorporated; 7-meG labeled with 3H was used to cap the mRNA. A fraction of the sample was run on a gel and confirmed that radiolabeled capped transcripts had indeed been produced. The remainder of mRNA was incubated with wheat germ cell extract containing ribosomes to allow binding of the mRNA to ribosomes. The sample was deposited at the top of a sucrose density gradient and spun in a centrifuge. Surprisingly, neither label (32P nor 3H) comigrated with the ribosome fraction; the ribosomes did migrate as expected. What is the most likely reason for this result?
