Janus kinase

The name is taken from the two-faced Roman god of beginnings, endings and duality, Janus, because the JAKs possess two near-identical phosphate-transferring domains.

[4] The activated STATs dissociate from the receptor and form dimers before translocating to the cell nucleus, where they regulate transcription of selected genes.

They are also being studied in psoriasis, polycythemia vera, alopecia, essential thrombocythemia, ulcerative colitis, myeloid metaplasia with myelofibrosis and vitiligo.

Phosphorylation of these dual tyrosines leads to the conformational changes in the JAK protein to facilitate binding of substrate.

The amino terminal (NH2) end (JH4-JH7) of Jaks is called a FERM domain (short for band 4.1, ezrin, radixin and moesin); this domain is also found in the focal adhesion kinase (FAK) family and is involved in association of JAKs with cytokine receptors and/or other kinases.

Overview of signal transduction pathways involved in apoptosis
The JAK-STAT system consists of three main components: (1) a receptor (green), which penetrates the cell membrane; (2) Janus kinase (JAK) (yellow), which is bound to the receptor, and; (3) Signal Transducer and Activator of Transcription (STAT) (blue), which carries the signal into the nucleus and DNA. The red dots are phosphates. After the cytokine binds to the receptor, JAK adds a phosphate to (phosphorylates) the receptor. This attracts the STAT proteins, which are also phosphorylated and bind to each other, forming a pair (dimer). The dimer moves into the nucleus, binds to the DNA, and causes transcription of genes. Enzymes that add phosphate groups are called protein kinases.
Domain structure of Janus kinases, JH = JAK homology domain