Atomic force microscopic study on topological structures of pBR322 DNA.
Plasmid pBR322 DNA (0.5 mg/mL) isolated from Escherichia coli HB101 was suspended in Tris-HCI-EDTA (1 mol/L-0.1 mol/L, pH 8.5); then a drop of the above solution was deposited on freshly cleaved mica substrate. After adsorption for about 1 mm, the sample was stained with phosphotungstic acid. The residual solution was removed with a piece of filter paper. Afterwards the sample was imaged with a home-made atomic force microscope (AFM) in air. The AFM images of pBR322 DNA with a molecular resolution have been obtained. These images show that pBR322 DNA exists in several different topological structures: (i) relaxed circular DNA with a different diameter; (ii) supercondensed DNA with different particle sizes; (iii) dimeric catenane connected by one relaxed circular molecule and another close-compacted molecule which might be either supercoiled or intramolecular knotted form; (iv) oligomeric catenane with multiple irregular molecules in which DNA is interlocked into a complex oligomer; (v) possibly-existing intermediates formed from monomer to oligomer.
Zhang
P
P
STM Laboratory, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China.
Bai
C
C
Cheng
Y
Y
Fang
Y
Y
Wang
Z
Z
Huang
X
X
D004269:DNA, Bacterial / Q000302:isolation & purification / Q000648:ultrastructure*; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D018625:Microscopy, Atomic Force; D010957:Plasmids / Q000302:isolation & purification / Q000648:ultrastructure*
D004269:DNA, Bacterial