Reversible arrest of Chinese hamster cells in G1 by partial deprivation of leucine

Abstract

The cell cycle of Chinese hamster cells in culture can be arrested by removal of leucine from the medium. When a growing culture is completely deprived of leucine, part of the cell population accumulates in G1, but some cells are arrested in the S and G2 periods. When a trace of leucine (0.1% or 1.0% of the normal concentration) is left in the medium, more of the cells accumulate in G1 during a 36-h period of deprivation. The maximum G1 accumulation has been obtained using 0.1% of the normal leucine concentration with a culture of low cell density. Release of the culture by addition of leucine is followed by a moderate amount of synchrony in DNA synthesis and cell division. The experiments show that cells can complete the S, G2, and division periods with levels of leucine in the medium that do not permit cells to traverse through G1. This differential sensitivity of G1 appears to be positioned several hours before the initiation of DNA synthesis. In addition, the progress of cells in middle and late G1 at the time of leucine withdrawal is cancelled, and such cells revert to an earlier position in G1 where they remain in cycle arrest unless released by reprovision of leucine.