It can be helpful as typified by its use in a specific type of PCR to do such things as clone cDNAs, but its most troubling form is one coded for by the pol gene in a certain disease.  
Commercially available samples of this protein are obtained from one of two sources: Avian myeloblastosis virus or Moloney murine leukemia virus.  It was initially discovered in David Temin's experiment involving actinomycin D applications to cultures of cells infected with Rous sarcoma virus.  It can be helpful as typified by its use in a specific type of PCR to do such things as clone cDNAs, but its most troubling form is one coded for by the pol gene in a certain disease.  FTP, identify this enzyme found in retroviruses, which synthesizes DNA from an RNA template.
Commercially available samples of this protein are obtained from one of two sources: Avian myeloblastosis virus or Moloney murine leukemia virus.  
reverse transcriptase or RNA-dependent DNA polymerase