Ste5 is a prototype of scaffold proteins that regulate activation of mitogen-activated protein kinase (MAPK) cascades in all eukaryotes. Ste5 associates with many proteins including Gbg (Ste4/Ste18); (Ste4), Ste11 MAPKKK, Ste7 MAPKK, Fus3 and Kss1 MAPKs, Bem1, Cdc24. Here we show that Ste5 also associates with heat shock protein 70 chaperone (Hsp70) Ssa1 and that Ssa1 and its ortholog Ssa2 are together important for Ste5 function and efficient mating responses. The majority of purified overexpressed Ste5 associates with Ssa1. Loss of Ssa1 and Ssa2 has deleterious effects on Ste5 abundance, integrity, and localization particularly when Ste5 is expressed at native levels. The status of Ssa1 and Ssa2 influences Ste5 electrophoresis mobility and formation of high molecular weight species thought to be phosphorylated, ubiquitinylated and aggregated and lower molecular weight fragments. A Ste5 VWA domain mutant with greater propensity to form punctate foci has reduced predicted propensity to bind Ssa1 near the mutation sites and forms more punctate foci when Ssa1 Is overexpressed, supporting a dynamic protein quality control relationship between Ste5 and Ssa1. Loss of Ssa1 and Ssa2 reduces activation of Fus3 and Kss1 MAPKs and FUS1 gene expression and impairs mating shmoo morphogenesis. Surprisingly, ssa1, ssa2, ssa3 and ssa4 single, double and triple mutants can still mate, suggesting compensatory mechanisms exist for folding. Additional analysis suggests Ssa1 is the major Hsp70 chaperone for the mating and invasive growth pathways and reveals several chaperone-network proteins required for mating morphogenesis.

A bank promises to lend several billion dollars to fund a buyer’s purchase of a target company. The buyer enters into a merger agreement with the target. Thereafter, the economy plummets, and the bank decides that breaching its contract with the buyer will cost less than performing. The buyer seeks specific performance. The target also sues the bank, alleging tortious interference with the merger agreement. Billions of dollars are on the line. This is the reality lived by many investment banks that committed to fund leveraged buyouts during the recent economic downturn. Most of these matters were resolved in private settlements to avoid the possibility of crippling tort liability and publicly airing the messy details of the targets’ poor financial circumstances. The judicial decisions that do exist reveal a myopic view of the relationship between the buyer’s specific performance claim against the bank, on the one hand, and the target’s tort claim against the bank, on the other. By treating these claims as substantively distinct, courts threaten to impose an inefficient liability rule for the bank’s allegedly tortious conduct (including the possibility of punitive damages) and an equally inefficient property rule for the bank’s alleged breach of contract (specific performance). Courts must take a singular view of the combined costs and efficiencies created by the buyer’s and target’s individual claims to properly determine the appropriate remedy for the bank’s conduct.