when phi x174 viral dna containing an amber mutation ( am3 ) is primed with a single restriction endonuclease fragment , copied in vitro with pol i and then expressed in e. coli spheroplasts ( weymout , l. a. , and loeb , l. a . ( 1978 ) proc . natl . acad . sci . u. s. a . 75 , 1924 ) , the reversion frequency of this dna is greater than that of uncopied dna .
C0012939
viral dna
C0012854
dna