Transmission electron microscopy and scanning force microscopy of poly r(A-U) and poly r(A-U)-ethidium bromide.
Transmission electron microscopy and scanning force microscopy of negative-stained, carbon-coated replica and mica-adsorbed preparations of 200 microM poly r(A-U) and 50 microM ethidium bromide/200 microM poly r(A-U) have been employed to evaluate ethidium-induced changes in poly r(A-U) topology. Poly r(A-U) alone exhibits elongated conformations 85-115 nm in length that possess a number of hairpin loops as well as single-stranded domains. While the double-stranded domains are found predominately at the base of the hairpin loops (diameter = 5-30 nm), other rod-like (presumably double-stranded) regions ranging from 25-80 nm in length are present in other portions of the poly r(A-U). In contrast with the poly r(A-U) alone, the EB/poly r(A-U) combination appears as a heterogeneous population of condensed structures whose lengths and widths vary from 12-88 nm and 15-45 nm, respectively. These conformational changes are due to a number of factors, including the displacement of ordered water surrounding the poly r(A-U) and charge shielding of the phosphate groups of the poly r(A-U) upon the binding of the ethidium.
Gilloteaux
J
J
Department of Anatomy, Lake Erie College of Osteopathic Medicine, PA 16509-1025, USA.
Jamison
J M
JM
Zenhausern
F
F
Adrian
M
M
Summers
J L
JL
D000225:Adenine / Q000737:chemistry; D004996:Ethidium / Q000737:chemistry*; D018625:Microscopy, Atomic Force / Q000379:methods*; D008854:Microscopy, Electron / Q000379:methods*; D008956:Models, Chemical; D008968:Molecular Conformation; D011063:Poly A-U / Q000737:chemistry*; D011108:Polymers; D012330:RNA, Double-Stranded / Q000737:chemistry / Q000648:ultrastructure*; D014498:Uracil / Q000737:chemistry
D011108:Polymers; D012330:RNA, Double-Stranded; D011063:Poly A-U; D014498:Uracil; D004996:Ethidium; D000225:Adenine