The discovery of reverse transcriptase (RT) over 20 years ago was important for two reasons.First,it suggested that genetic information could flow back and forth from DNA to RNA and from RNA to DNA,thus explaining the replication of some viruses.Second,the presence of RT suggested a mechanism for shift from an RNA-based life to one revolving around DNA double helix.We have extracted and purified of RT with 3 step chromatography.in this method E.Coli-107 was grown at 37oC in 2 liters LB media at 300 rpm agitation and lvvm aeration.After 3-4 h,it induces with IPTG and let grow 4 h to late log phase.The cell harvested by centrifuge in 3000 rpm during 20 min.The pellet suspended in lysis buffer,sonicated and centrifuged at 100000g for 1h.