sentence: The main catalytic property distinguishing Nfo from XthA is the lack of 3 ′ exonuclease activity as described in the recent review article ( 5 ) and also in the textbook ( 14 ) , although a report in the year 2003 showed that Nfo and its homolog from the hyperthermophilic eubacteria , Thermotoga maritime and Thermus thermophilus , have the exonuclease activity ( 15,16 ) .