The unusual and dynamic character of PX-DNA.
Bottom Line: Some of the structural features of the molecule have been noted previously, but the structure requires further characterization.Here, we report atomic force microscopic characterization of PX molecules that contain periodically placed biotin groups, enabling the molecule to be labeled by streptavidin molecules at these sites.In comparison with conventional double stranded DNA and with antiparallel DNA double crossover molecules, it is clear that PX-DNA is a more dynamic structure.
Affiliation: Department of Chemistry, New York University, New York, NY 10003, USA.Show MeSH
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Mentions: If the structure of PX-DNA were inconsistent with the B-form DNA conformation, the labeling sites chosen above might not be optimal. One solution to this problem is moving all the labels in either the 3′ or 5′ direction by a fixed small number of nucleotides so as to rotate them by a few nucleotide twist intervals. The rotation is expected eventually to place the conjugates at sites where a clear zigzag could form. Figure 3A illustrates the idea behind this experiment. Considering the rotation per base pair in B-form DNA is roughly equal to 34–36°, moving the labels by a maximum of 3 nt should be sufficient to titrate the required angular range. We have made and tested six different systems, and the AFM results are summarized in Figure 3B. Among all the results, only moving the labels by 2 nt in the 5′ direction sometimes generates a zigzag PX-DNA pattern (32%), whereas all the other five variants largely produce linear PX-DNA streptavidin patterns. Although a small number of barely zigzag molecules were also observed from each of the other variants, the percentages of the absolutely linear patterns from them are all higher than 90%.
Affiliation: Department of Chemistry, New York University, New York, NY 10003, USA.