Abstract: Budding yeast contains one protein kinase C (PKC) isozyme encoded by the essential gene PKC1. Pkc1 is activated by the small GTPase Rho1 and plays a central role in the Cell Wall Integrity (CWI) signaling pathway. This pathway primarily acts to remodel the cell surface throughout the normal lifecycle and upon various environmental stresses. The pathway is heavily branched with multiple non-essential branches feeding into and out of the central essential Rho1-Pkc1 module. In an attempt to identify novel components and modifiers of CWI signaling, we determined the synthetic lethal genetic network around PKC1 using dominant negative synthetic genetic array (DN-SGA) analysis. The resulting 21 mutants are hypersensitive to lowered Pkc1 activity. The corresponding 21 non-essential genes are closely related to CWI function: fourteen behave in a chemical-genetic epistasis test as acting in the pathway of which six encode known components. Twelve of the 21 null mutants display elevated CWI reporter activity consistent with the pathway being activated by and compensating for loss of the gene products. Four of the 21 mutants display low CWI reporter activity consistent with the pathway being compromised in these mutants. One of the latter lacks an uncharacterized SEL-1 domain-containing protein Ack1(Ydl203c) that we find modulates pathway activity. Epistasis analysis places Ack1 upstream of Pkc1 in the CWI pathway and dependent on the upstream Rho1 GTP exchange factors Rom2 and Tus1. Overall, the synthetic genetic network around PKC1 directly and efficiently identifies known and novel components of protein kinase C signaling in yeast.