SSK22 (YCR073C, UniProt P25390) curation notes

Identity

• Serine/threonine-protein kinase SSK22 (MAP kinase kinase kinase SSK22), STE family MAPKKK; kinase domain aa 1034-1310 [file:yeast/SSK22/SSK22-uniprot.txt]. Paralog of SSK2 (lacks Ssk2's extra N-terminal ~176 aa).
• Low abundance (56 molecules/cell) [file:yeast/SSK22/SSK22-uniprot.txt "Present with 56 molecules/cell in log phase SD medium."].

Function: redundant MAP3K of the Sln1 branch

• Pbs2 activation by Ssk2 and Ssk22 PMID:7624781.
• Either MAPKKK suffices; complementation of ssk2 ssk22 ste50 by SSK22 PMID:9742096.
• Ssk22 kinase domain binds Pbs2 docking site RSD-I PMID:12853477.
• Ssk1 binds Ssk2/Ssk22 N-terminal regulatory domain PMID:18573873.
• Unlike Ssk2, Ssk22 activation strictly depends on Ssk1; weaker than Ssk2 in salt stress [PMID:23457455 "The activation of Ssk22p, on the other hand, was totally dependent on Ssk1p."; "Actually, upon nonionic osmotic stress, the Ssk2p and Ssk22p can function equally well."].
• Ssk22 not required for Ssk2's actin recovery role; Ssk22 fragment does not bind actin in two-hybrid PMID:12181352.
• Any Ssk22-specific function unknown PMID:18573873.

Localization

• No Ssk22-specific imaging; GOA has ND for CC plus IEA cytoplasm. Operates with cytoplasmic Ssk1/Pbs2.

Annotation decisions

• Kinase MF rows (HDA, IEA, ISS, EC, Rhea): ACCEPT.
• GO:0038066 rows: ACCEPT.
• Protein binding x3 (Ssk1; HTP): REMOVE (interaction real, no informative MF term).
• NEW GO:0007234 osmosensory signaling via phosphorelay pathway: Ssk22 is directly activated by Ssk1 like Ssk2 (which carries this term by IGI/IPI); the Ssk1 dependence of Ssk22 is shown in PMID:23457455. Comparator: Ssk2 (same role) carries it; Pbs2/Hog1 (further downstream) do not.