Enzymes. Enzymes used and the sources were as follows: endodeoxyribonucleases (deoxyribonucleate oligonucleotidohydrolase, EC 3.1.4.30) EcoRI and BamHI (R. Reeder) and HindIII (D. Brown); DNA nucleotidylexotransferase (nucleosidetriphosphate:DNA deoxynucleotidylexotransferase, EC 2.7.7.31)