Kinetics curves (relative ODN concentrations as a function of time) of the 3′ hydrolysis of a 25 μmol/L solution of PO2 on incubation at 37°C in RPMI 1640 containing 2.5% HS. PO2-1, PO2-2, and PO2-3 represent, respectively, the PO2 sequence minus 1, 2, and 3 deoxyribonucleotides at the 3′ end. PO2 half-life (38 hours) is indicated by the position of the two arrows. The dashed curve (symetrical to the PO2 curve) indicates the theoretical TMP relative concentration generated by hydrolysis of the PO2 3′ very last linkage. The PO2-2 curve represents also the maximal d-CMP relative concentration generated by hydrolysis of the PO2-1 3′ very last position.