Changes in the free and rough endoplasmic reticulum-bound ribosomes of Ehrlich ascites cancer cells during the cell cycle

The amount of rough endoplasmic reticulum (RER) and associated polyribosomes changes during the cell cycle. We describe here the amount and activity of free and RER-bound ribosomes of Ehrlich ascites cancer cells. RER does not exist during the G1, G2 and M phases, it appears in the early S phase and decreases in the second half of S. The formation of RER during the S phase and the S phase RER-found ribosomes may be related to the biosynthesis of histones, some fundamental non-histonic nuclear proteins, and enzymes involved in DNA replication and several metabolic reactions.