A) Deletions of genes that act in the same pathway result in cell growth
greater than expected from the growth defects of the individual mutants. DNA repair
proteins Rad52, Rad51 and Rad54 function interdependently in the RAD51-dependent
double-strand break repair pathway. Removal of any one of these results in a dysfunctional
pathway, and thus removal of the remaining two proteins affects viability less severely
than expected for unrelated proteins. B) Two proteins suppress a rogue
function of a third protein. Deletion of the suppressing pair (A and C) results in cell
sickness due to the rogue function of the third protein (B), but cell growth is restored
upon deletion of the responsible gene (BΔ). Cells lacking one of the components of
the CAF-1 histone H3-H4 chaperone display severe sickness in the absence of one of the
HIRA complex components, but suppression is achieved by removal of the second chaperone,
Asf1. We interpret this as an indication that Asf1 acts in a detrimental fashion when both
CAF-1 and HIRA are missing.