Receptor-tyrosine kinases (RTK) are transmembrane proteins allowing the transduction of extracellular signals. On the binding of an extracellular ligand, such as a hormone, the receptor dimerises. This improves the kinase activity of the RTK, allowing the phosphorylation of the receptor and activation of the kinase activity. The receptor is then able to phosphorylate second messaging molecules within the cell, allowing control of transcription.
This is a significant signalling pathway, allowing hormonal transcriptional control.