anosyl) thymine. It was fully characterised by NMR, UV and mass spectrometry. Taq polymerase enzymaticincorporation of this nucleotide analogue into DNA fragments was investigated. Morpholino thymidine-5′-triphosphate was incorporated in a base-specific process and acted as a novel chain terminator in DNA sequencing, similarly to the corresponding dideoxynucleotide.