The general control of amino acid biosynthesis was shown to play an important role in the coordination between cell growth and cell division under amino acid limitations. Mutant strains defective in this regulatory system, as studied here mainly with mutant strain RH375 (ndr1-1), showed excessive and aberrant cell growth under mild limitation, and rapid loss of cell viability under severe amino acid limitation. Furthermore, wild-type (NDR1) cells were able to derepress, or at least maintain, levels of enzymes subject to the general control under amino acid limitations. The ndr1-1 mutant cells showed significantly decreased enzyme levels under these conditions. The loss of viability of ndr1-1 mutant cells was not due to inability to accumulate at ‘Start’ under amino acid limitation. In conclusion, we postulate that the aberrant behaviour of ndr-mutant cells is due to an inability to maintain adequate levels of amino acid biosynthetic enzymes throughout the mitotic cell cycle.
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