This family represents a conserved region of eukaryotic Fas-activated serine/threonine (FAST) kinases (EC:2.7.1.-) that contains several conserved leucine residues. FAST kinase is rapidly activated during Fas-mediated apoptosis, when it phosphorylates TIA-1, a nuclear RNA-binding protein that has been implicated as an effector of apoptosis [1]. Note that many family members are hypothetical proteins. This subdomain is often found associated with the FAST kinase-like protein, subdomain 2.

1: Fas-activated serine/threonine kinase (FAST) phosphorylates TIA-1 during Fas-mediated apoptosis. Tian Q, Taupin J, Elledge S, Robertson M, Anderson P; J Exp Med 1995;182:865-874. PMID:7544399