In response to viral infections, various pattern recognition receptors (PRRs) 
are activated for the production of type I interferon (IFN I). As a center of 
these receptor responses, TANK binding kinase-1 (TBK1) activates interferon 
regulatory factor 3 (IRF3). SRC is a member of Src family kinases (SFK) which 
participates in TBK1-mediated IFN I signaling pathway. In mammals, the 
immunological function of SRC is depended on its interaction with TBK1. To date, 
SRC has not been studied in fish. In this paper, we cloned the ORF of grass carp 
(Ctenopharyngodon idellus) SRC (CiSRC). CiSRC has a closer relationship with 
Sinocyclocheilus rhinocerous SRC (SrSRC). The expression level of CiSRC was 
significantly up-regulated following poly (I:C) stimulation in grass carp 
tissues and cells. Subcellular localization results showed that CiSRC is located 
both in the cytoplasm and nucleus, while CiTBK1 is only located in the cytoplasm 
of CIK cells. When GFP-CiSRC and FLAG-CiTBK1 were co-transfected into CIK cells, 
we found that they were co-localized in the cytoplasm. GST-pulldown and 
Co-immunoprecipitation analysis revealed that CiSRC and CiSRC tyrosine kinase 
domain deletion mutant (SRC-ΔTyrkc) can interact with CiTBK1, respectively. 
CiSRC promotes the phosphorylation of CiTBK1. Furthermore, the phosphorylation 
of TBK1 is more strongly under poly (I:C) stimulation. We also demonstrated that 
SRC can up-regulate IFN I expression. These results above unraveled that CiSRC 
initiates innate immune response by binding to and then up-regulating the 
phosphorylation of TBK1.