History of The Restriction Point
Originally, Temin showed that chicken cells reach a point at which they are committed to replicate their DNA and are not dependent on extracellular signals About 20 years later, in 1973, Arthur Pardee demonstrated that a single restriction point exists in G1. Previously, G1 had been defined simply as the time between mitosis and S phase. No molecular or morphological place-markers for a cell's position in G1 were known. Pardee used a double-block method in which he shifted cells from one cell cycle block (such as critical amino-acid withdrawal or serum-withdrawal) to another and compared each block’s efficiency at preventing progression to S phase. He found that both blocks in all cases examined were equally efficient at blocking S phase progression, indicating that they must all act at the same point in G1, which he termed the “restriction point,” or R-point
In 1985, Zetterberg and Larsson discovered that, in all stages of the cell cycle, serum deprivation results in inhibition of protein synthesis. Only in postmitotic cells (i.e. cells in early G1) did serum withdrawal force cells into quiescence (G0). In fact, Zetterberg found that virtually all of the variability in cell-cycle length can be accounted for in the time it takes the cell to move from the restriction point to S phase.
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