Final answer:
The least effective experimental approach to determine the localization of pRB protein within a cell is option b) using a fluorescent probe that hybridizes to rb transcripts.
Step-by-step explanation:
The experimental approach that would be LEAST effective in determining the localization of pRB (PROTEIN) within a cell is Option B) Use of a fluorescent probe that hybridizes to rb transcripts. Using a fluorescent probe that hybridizes to rb transcripts would not directly tell us the localization of pRB protein within the cell. Instead, it would provide information about the location of rb transcripts, which may or may not correlate with the actual location of the protein. To determine the localization of pRB protein, it would be more effective to use techniques such as fusion of a fluorescent tag to pRB (Option A), cellular fractionation to isolate different organelles (Option C), or pull down of pRB and identification of interacting proteins by mass spectrometry (Option D).