Solution AFM studies of human Swi-Snf and its interactions with MMTV DNA and chromatin.
ATP-dependent nucleosome remodeling complexes are crucial for relieving nucleosome repression during transcription, DNA replication, recombination, and repair. Remodeling complexes can carry out a variety of reactions on chromatin substrates but precisely how they do so remains a topic of active inquiry. Here, a novel recognition atomic force microscopy (AFM) approach is used to characterize human Swi-Snf (hSwi-Snf) nucleosome remodeling complexes in solution. This information is then used to locate hSwi-Snf complexes bound to mouse mammary tumor virus promoter nucleosomal arrays, a natural target of hSwi-Snf action, in solution topographic AFM images of surface-tethered arrays. By comparing the same individual chromatin arrays before and after hSwi-Snf activation, remodeling events on these arrays can be monitored in relation to the complexes bound to them. Remodeling is observed to be: inherently heterogeneous; nonprocessive; able to occur near and far from bound complexes; often associated with nucleosome height decreases. These height decreases frequently occur near sites of DNA release from chromatin. hSwi-Snf is usually incorporated into nucleosomal arrays, with multiple DNA strands entering into it from various directions, + or - ATP; these DNA paths can change after hSwi-Snf activation. hSwi-Snf appears to interact with naked mouse mammary tumor virus DNA somewhat differently than with chromatin and ATP activation of surface-bound DNA/hSwi-Snf produces no changes detectable by AFM.
Wang
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Arizona Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA.
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Lindsay
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D000255:Adenosine Triphosphate / Q000737:chemistry; D002843:Chromatin / Q000737:chemistry / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry* / Q000378:metabolism; D002875:Chromosomes / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics*; D018625:Microscopy, Atomic Force / Q000379:methods*; D009687:Nuclear Proteins / Q000737:chemistry; D009707:Nucleosomes / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism
D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D009687:Nuclear Proteins; D009707:Nucleosomes; D014157:Transcription Factors; D000255:Adenosine Triphosphate; D004247:DNA