Protein factors in extracts of ribosomes isolated from L-929 cells during various phases of the cell cycle

Centrifugal elutriation has been utilized in order to separate cultures of L-929 fibroblasts into subpopulations containing cells at different stages of the cell cycle. The subpopulations were characterized by Coulter counter volume determination, [3H]thymidine label into DNA and flow cytometry. When a population of early G1 cells was returned to roller culture it was shown to progress through the cell cycle in a synchronous manner. Ribosomal factor extracts were prepared from cells at various phases during the cell cycle. The amounts of protein in the extracts varied greatly, being lowest in early G1 phase and showing a peak during S phase. Polyacrylamide gel electrophoresis demonstrated that there were differences in the protein species present in the extracts. Some proteins were present in the same amounts throughout the cell cycle, whereas others appeared to show a form of cyclical behaviour.