<p>These domains display a core structure consisting of a closed bundle of four helices in a left-handed twist, with two crossover connections. Proteins containing such domains include long-chain cytokines, such as leukaemia inhibitory factor (LIF) [<cite idref="PUB00013237"/>], the growth hormone somatotropin [<cite idref="PUB00013316"/>], interleukin-6 [<cite idref="PUB00013238"/>] and leptin [<cite idref="PUB00013399"/>]; short-chain cytokines, such as erythropoietin [<cite idref="PUB00013240"/>], stem cell factor (SCF) [<cite idref="PUB00013241"/>], macrophage colony-stimulating factor (M-CSF) and interleukin-2, -3, -4, -5 and -13; and interferons/interleukin-10.</p> Four-helical cytokine-like, core