Biological DNA modifications have been studied for many years, and much is known about their distribution and the enzymes involved. Well-known base modifications are C-5-methylcytosine (m5C), N4-methylcytosine (m4C) and N6-methyladenine (m6A) . These are widely distributed in cellular organisms, particularly prokaryotes. Other base modifications have long been known in bacteriophage, prominently 5-hydroxymethylcytosine (hm5C) and derivatives of it with sugar residues attached (ghm5C), and 5-hydroxymethyluracil (hm5U). Is there are any other modified bases in case of T-even Bacteriophages?