Location, location, location. It has been, and remains, one of the best initial clues to understand the function of a protein or process. The same was true for those trying to localize protein synthesis in the 1950s and 1960s, but their experiments came with a twist. This early in the history of cell biology, the localization effort was not far behind, or even inspired, the definition and naming of the locations.
The cells of choice were pancreatic or liver cells that were furiously churning out secreted proteins. Littlefield et al. (1955) made a promising start by showing that radioactive amino acids accumulated first in the detergent-resistant particles of the microsomes (i.e., the ribosomes) before moving into the membranous portion. The authors felt confident to state that “the cytoplasmic ribonucleoprotein particles are the site of initial incorporation of free amino acids into protein.
Radioactive leucine is...
