Enzymatic Method for the Synthesis of Long DNA Sequences with Multiple Repeat Units

Multiply Modified Repeating DNA Templates for Production of Novel DNA-Based Nanomaterial

Here, we report synthesis of long (thousands of base pairs), uniform double-stranded (ds) DNA comprising short (6-15 base pairs) tandem repeats. The synthesis method is based on self-assembly of short (6-15 bases) half-complementary 5'-end phosphorylated single-stranded oligonucleotides into long ds polymer molecules and covalent association of the oligonucleotide fragments in the polymer by DNA ligase to yield complete non-nicked ds DNA. The method is very flexible in regard to the sequence of the oligonucleotides and their length. Human telomeric DNA comprising thousands of base pairs as well as methylated, mismatched, and fluorescent dye-modified uniform dsDNA molecules can be synthesized. We have demonstrated by high resolution frequency-modulation atomic force microscopy that the structure of DNA containing mismatches is strongly different from that of the non-mismatched one. The DNA molecules comprising groups capable of anchoring metal particles and other redox active elements along the whole length of the nucleic acid polymer should find use as wires or transistors in future nanoelectronic applications.

Self-Priming Enzymatic Fabrication of Multiply Modified DNA

The self-priming synthesis of multiply modified DNA by the extension of repeating unit duplex "oligoseeds" provides a source of versatile DNA. Sterically-demanding nucleotides 5-Br-dUTP, 7-deaza-7-I-dATP, 6-S-dGTP, 5-I-dCTP as well as 5-(octadiynyl)-dCTP were incorporated into two extending oligoseeds; [GATC]₅ /[GATC]₅ and [A₄ G]₄ /[CT₄ ]₄ . The products contained modifications on one or both strands of DNA, demonstrating their recognition by the polymerase as both template (reading) and substrate (writing). Nucleobase modifications that lie in the major groove were reliably read and written by the polymerase during the extension reaction, even when bulky or in contiguous sequences. Repeat sequence DNA over 500 bp long, bearing four different modified units was produced by this method. The number, position and type of modification, as well as the overall length of the DNA can be controlled to yield designer DNA that offers sequence-determined sites for further chemical adaptations, targeted small molecule binding studies, or sensing and sequencing applications.