Kinase suppressor of Ras (Ksr) and MAP kinase kinase kinase (MEKK3) are integral members of the MAP kinase pathway. Ksr is a conserved protein that positively regulates Ras signaling and may function as a scaffold for Raf, MEK and ERK. There are two types of Ksr proteins: Ksr-1 and Ksr-2. Ksr-2 plays a key role in Ras-mediated signaling during germline meiotic progression and functions redundantly with Ksr-1 during the development of the excretory system pathway, hermaphrodite vulva, and male spicules. Ksr-2 also functions as a negative regulator of the MEKK3-mediated activation of the MAP kinase pathways (specifically ERK and JNK) and of the NF?B pathways, and it simultaneously inhibits MEKK3-mediated Il-8 production.