Signal transducer and activator of transcription 3 also known as STAT3 is a transcription factor

Transcription factor

In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...

 which in humans is encoded by the STAT3 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

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The protein encoded by this gene is a member of the STAT protein

STAT protein

The STAT protein regulates many aspects of growth, survival and differentiation in cells...

 family. In response to cytokines and growth factors, STAT family members are phosphorylated by receptor-associated kinases

Tyrosine kinase

A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to a protein in a cell. It functions as an "on" or "off" switch in many cellular functions....

 and then form homo- or heterodimers that translocate to the cell nucleus, where they act as transcription activators.