NCK (or non-catalytic region of tyrosine kinase adaptor protein 1) is an adaptor protein that is located in the cytoplasm and involved in transducing signals from receptor tyrosine kinases to downstream signal recipients such as RAS. NCK is a signaling and transforming protein that contains Src homology 2 and 3 (SH2 and SH3) domains. NCK functions by coupling tyrosine phosphorylation via SH2 domains to downstream effectors through SH3 domains. Furthermore, NCK couples tyrosine phosphorylation guidance signals to cytoskeletal events required for the ipsilateral projections of spinal cord neurons and for normal limb movement.