Fas-activated serine/threonine kinase is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

that in humans is encoded by the ''FASTK''

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

. The protein encoded by this gene is a member of the serine/threonine

protein kinase A protein kinase is a kinase which selectively modifies other proteins by covalently adding phosphates to them (phosphorylation) as opposed to kinases which modify lipids, carbohydrates, or other molecules. Phosphorylation usually results in a fu ...

family. This kinase was shown to be activated rapidly during Fas-mediated apoptosis in

Jurkat cells Jurkat cells are an immortalized line of human T lymphocyte cells that are used to study acute T cell leukemia, T cell signaling, and the expression of various chemokine receptors susceptible to viral entry, particularly HIV. Jurkat cells can pr ...

. In response to

Fas receptor The Fas receptor, also known as Fas, FasR, apoptosis antigen 1 (APO-1 or APT), cluster of differentiation 95 (CD95) or tumor necrosis factor receptor superfamily member 6 (TNFRSF6), is a protein that in humans is encoded by the ''FAS'' gene. Fas ...

ligation, it

phosphorylates In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, whi ...

the apoptosis-promoting nuclear RNA-binding protein TIA1. The encoded protein is a strong inducer of

lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...

apoptosis. Two

transcript variant Alternative splicing, or alternative RNA splicing, or differential splicing, is an alternative splicing process during gene expression that allows a single gene to code for multiple proteins. In this process, particular exons of a gene may be in ...

s encoding different

isoform A protein isoform, or "protein variant", is a member of a set of highly similar proteins that originate from a single gene or gene family and are the result of genetic differences. While many perform the same or similar biological roles, some iso ...

s have been found for this gene. The longer one is located in the cell nucleus and cytoplasm, and the shorter one is 34 amino acids at the N-terminus, which is transported to the mitochondrion. The mitochondrial FASTK isoform localizes in the mitochondrial granules, where it interacts with the GRSF1 protein and binds to mt-mRNA ND6, the template of the only protein encoded on the light strand of the mitochondrial genome. In the case of FASTK deletion, it was observed loss of ND6 mt-mRNA and a 50-60% decrease in the activity of complex I of the respiratory chain. However, overexpression of this protein resulted in the stabilization of ND6 mt-mRNA Other variants exist, but their full-length natures have not yet been determined.

References

Further reading