This product is expressed by E. coli, and the source of the expressed gene is T4 bacteriophage. Since T4 DNA polymerase has both 5'→3' DNA polymerase activity and 3'→5' DNA exonuclease activity, it can be used to blunt the 5' protruding ends or trim the 3' protruding ends, synthesize labeled DNA probes by displacement reaction, analyze the initiation points of mRNA transcription by primer extension method, synthesize of the second strand during site-directed mutagenesis, clone ligation-independent PCR product, etc. The 3'→5' DNA exonuclease activity of this T4 DNA polymerase is about 100-1,000 times higher than that of Klenow Fragment, and it is more active for single-stranded DNA than double-stranded DNA. The enzyme does not contain the exonuclease activity of 5'→3' DNA. It can be inactivated by heating at 70 ℃ for 10 minutes, and metal ion chelators can inhibit its activity.