Fig.1

PCR amplification result of chicken DDX21 geneM， DL5000 DNA Marker； 1， PCR product of chicken DDX21 gene； 2， Negative control"

Fig.2

Identification of positive clone of pMD18T-chDDX21 plasmidM， DL5000 DNA Marker； 1， Negative control； 2 and 3， Positive clone"

Fig.3

Similarity alignment results of amino acid sequence of DDX21"

Table 1

Amino acid sequence similarity analysis of the DEXDc，HELICc and GUCT domains of DDX21 protein in chicken and other species"

Fig.4

Phylogenetic tree based on DDX21 gene"

Fig.5

Schematic diagram of domain of chicken DDX21 protein"

Fig.6

Prediction of secondary structure of DDX21 protein in chickenThe lines from long to short represent beta sheet， alpha helix and random coil， respectively"

Fig.7

Prediction of tertiary structure of DDX21 protein in chicken"

Fig.8

Identification results of recombinant expression plasmid pET28a-chDDX21 by PCRM， DL5000 DNA Marker； 1， Negative control； 2， Positive plasmid"

Fig.9

Optimization results of IPTG induced concentrationM， Broad Range Rainbow Molecular Weight Marker （10-130 ku）； 1， Cacterial culture of empty vector； 2-7， The IPTG induction concentrations were 0， 0.1， 0.3， 0.5， 0.7 and 0.9 mmol/L， respectively"

Fig.10

Optimization results of IPTG induced timeM， Broad Range Rainbow Molecular Weight Marker （10-130 ku）； 1， Bacterial culture of empty vector； 2-7， IPTG induction for 8， 10， 12， 14， 16 and 18 h， respectively"

Fig.11

SDS-PAGE analysis of induced expression of chicken DDX21 recombinant proteinM， NcmColor Prestained Protein Marker （14-250 ku）； 1， Bacterial culture of empty vector； 2， Bacterial culture of recombinant protein without induction； 3， Bacterial culture of recombinant protein after induction； 4， Supernatant of sonicated bacterial culture after induction； 5， Pellet of sonicated bacterial culture after induction"

Fig.12

Western blotting analysis of induced expression of chicken DDX21 recombinant proteinM， Broad Range Rainbow Molecular Weight Marker （10-130 ku）； 1， Bacterial culture of empty vector； 2， Bacterial culture of recombinant protein without induction； 3， Bacterial culture of recombinant protein after induction； 4， Supernatant of sonicated bacterial culture after induction； 5， Pellet of sonicated bacterial culture after induction"

Fig.13

SDS-PAGE analysis of the purified chicken DDX21 recombinant proteinM， Color-Coded Prestained Protein Marker （14-250 ku）； 1， Flow through fractions； 2-4， Wash fractions 1-3， respectively； 5-8， Elution fractions 1-4， respectively"

Fig.14

Results of serum titer of chicken DDX21 polyclonal antibody"

Fig.15

Western blotting analysis of expression of DDX21 protein in tissues of healthy and infected chickens①A， The expression of DDX21 protein in tissues of healthy chickens； B， The expression of DDX21 protein in tissues of chickens infected with H9N2 subtype AIV. ②M， Broad Range Rainbow Molecular Weight Marker （10-130 ku）； 1， Bursa of Fabricius； 2， Liver； 3， Lung； 4， Heart； 5， Thymus； 6， Brain； 7， Spleen"