Figure 1.

Synthetic lethal interactions between tub1-724 and altered levels of Rbl2p: a model. Cells expressing tub1-724 as their sole source of α-tubulin die when Rbl2p is either absent or overexpressed. Those relationships are explicable if the heterodimer formed by the Tub1-724p (α*β) dissociates more readily than that formed by the wild-type Tub1p (αβ). In the presence of a normal complement of RBL2, the mutant cells would have a high concentration of free β-tubulin (β_free), which may be responsible for the conditional phenotypes of the mutant (e.g., benomyl supersensitivity). In the absence of Rbl2p, the activity of β_free would increase to toxic levels. In contrast, an excess of Rbl2p could bind to β-tubulin and so enhance dissociation of the mutant heterodimer, promoting dissociation to levels below those necessary for viability.