VISUALIZATION OF CIRCULAR DNA-MOLECULES LABELED WITH COLLOIDAL GOLD SPHERES USING ATOMIC-FORCE MICROSCOPY

We have imaged gold-labeled DNA molecules with the atomic force microscope (AFM). Circular plasmid DNA was labeled at internal positions by nick-translation using biotinylated dUTP. For visualization, the biotinylated DNA was linked to streptavidin-coated colloidal gold spheres (nominally 5 nm diam) prior to AFM imaging. Reproducible images of the labeled DNA were obtained both in dry air and under propanol. Height measurements of the DNA and colloidal gold made under both conditions are presented. The stability of the DNA-streptavidin colloidal gold complexes observed even under propanol suggests that this labeling procedure could be exploited to map regions of interest in chromosomal DNA.