3-DIMENSIONAL STRUCTURE OF HIV-1 REV PROTEIN FILAMENTS

The HIV-1 Rev protein facilitates the export of incompletely spliced a nd unspliced viral mRNAs from the nucleus. Rev polymerizes into two ty pes of filaments in vitro. In the presence of RNA, Rev forms poorly or dered structures, while in the absence of RNA it polymerizes into regu lar hollow filaments. We have determined the helical structure of the latter filaments by analysis of cryo-electron micrographs, taking into account STEM measurements of mass-per-unit-length. They are made up o f Rev dimers, arranged in a six-start helix, with 31 dimers in 2 turns , a pitch angle of 45 degrees, and an interstrand spacing of 3.8 nm. T hree-dimensional reconstruction at 2.1 nm resolution reveals a smooth outer surface and a featured inner surface, with outer and inner diame ters of similar to 14.8 and similar to 10.4 nm, respectively. The Rev dimer has a ''top-hat'' shape with a cylinder similar to 3.2 nm in dia meter and similar to 2.2 nm high, pointing inward: the thinner rim are as pack together to form the filament wall. Raman spectroscopy shows p olymerized Rev to have similar to 54% alpha-helix and 20-24% beta-shee t content, Electron microdiffraction of aligned filaments reveals a br oad meridional reflection at similar to (0.51 nm)(-1), suggesting appr oximate alignment of the alpha-helices with the filament axis. Based o n these data, a molecular model for the Rev filament is proposed.