STE kinase consists of three main families which sequentially activate each other to then activate the MAPK family. The STE7 family directly phosphorylate MAPKs, and are also known as MAP2K, MEK, or MKKs; STE11 members phosphorylate STE7 kinases and are called MAP3K, while many STE20 members (MAP4K) act on Ste11 kinases. The STE20 (MAP4K) family is the largest of the three and is divided into many subfamilies. Some are implicated in MAPK cascades, while others are not and may have completely distinct functions.
The name of STE is originally from the studies in Sacharomyces cerevisiae. STE kinases play an important role in MAP kinase pathways, which require a sequential protein kinase reaction to activate the next kinase in the pathway. MAP kinase play a central role in the transduction of various extra- and intracellular signals and are evolutionarily conserved from Trypanosomatids to mammals, but have also been lost secondarily in reduced kinomes.
The typical MAPK signaling pathways mediating the transmission of external signals to intra-cellular effector proteins.