Abstract: A new type of histidine tag expression vector was obtained on the basis of the vector T7 Select10-3b through gene recombination technology. The recombined vector was used to construct cDNA library as an effective method of screening open reading frame（ORF）. A His-Tag was inserted into multiple clone site of vector T7. The sequence of His-Tag was obtained by renaturation. In order to get infectious T7 phage, T7 packaging extracts was utilized to package recombined DNA. CDNA library was constructed using modified vector, and ORF was purified by Ni-nitrilotriacetate affjnity chromatography. DNA sequencing revealed that His-Tag was inserted into the expression vector accurately. Chemiluminescence immunoassay displayed that inserted His-Tag sequence could express accurate protein. Screening rate of ORF rised from 5.6% to 82%. It proved that vector T7 inserted His-Tag had important significance for ORF screening.

Key words: His-Tag, T7 phage, cDNA library, ORF