Question

Abstract #1
Histone H3 phosphorylation near the nucleosome dyad alters chromatin structure. Nucleosomes
contain ∼146 bp of DNA wrapped around a histone protein octamer that controls DNA accessibility to
transcription and repair complexes. Posttranslational modification (PTM) of histone proteins regulates
nucleosome function. To date, only modest changes in nucleosome structure have been directly
attributed to histone PTMs. Histone residue H3(T118) is located near the nucleosome dyad and can be
phosphorylated. This PTM destabilizes nucleosomes and is implicated in the regulation of transcription
and repair. Here, we report gel electrophoretic mobility, sucrose gradient sedimentation, thermal
disassembly, micrococcal nuclease digestion and atomic force microscopy measurements of two DNA–
histone complexes that are structurally distinct from nucleosomes. We find that H3(T118ph) facilitates
the formation of a nucleosome duplex with two DNA molecules wrapped around two histone octamers,
and an altosome complex that contains one DNA molecule wrapped around two histone octamers. The
nucleosome duplex complex forms within short ∼150 bp DNA molecules, whereas altosomes require at
least ∼250 bp of DNA and form repeatedly along 3000 bp DNA molecules. These results are the first
report of a histone PTM significantly altering the nucleosome structure.

1) Summarize Key Findings from the paper as conveyed by the Abstract.
2) Suggest an experimental approach that the authors may have taken to demonstrate each findings, and why.

Answer 1