Complementation between two temperaturesensitive mammalian cell mutants, each defective in the G₁ phase of the cell cycle

Two mammalian temperature-sensitive (ts) G₁cell cycle mutants of different species origin (Syrian hamster and mouse) have been tested for complementation using somatic cell hybrid analysis. All hamster-mouse hybrid clones tested were found to exhibit normal growth properties at the restrictive temperature, while neither mutant alone was capable of normal growth at this temperature. The two mutant lines therefore complement for growth in a somatic cell hybrid and most likely represent ts lesions in different cellular functions specific to the G₁ phase of the cell cycle.