Then-doctoral student Yupeng Zheng developed antibodies that recognize phosphorylation at the H1 sites cells use when they are not dividing. This enabled Zheng to discover that such "interphase" H1 phosphorylation is preferentially associated with genes when they are actually being transcribed.
"Histones are normally found all over the genome," Mizzen said, " and elucidating what is different about the nucleosomes on active genes versus those on repressed genes versus the rest of the genome, most of which is not protein-coding, is a central goal of current research in molecular biology."
Several core histone modifications are known to localize preferentially to active genes, Mizzen said. "But our work provides the first evidence that this is also true for H1 that is phosphorylated at specific sites."
Zheng also made a second surprising discovery. Using fluorescence microscopy to analyze cells, he noticed that the fluorescently labeled antibodies targeting phosphorylated H1 in non-dividing cells were lighting up the nucleolus, the region of the nucleus that is dedicated to transcribing ribosomal RNA, the special RNA upon which ribosomes are assembled.
"The ribosomal RNA genes are kept in the nucleolus and they're transcribed by a different enzyme system than the messenger RNAs that are transcribed from protein-coding genes," Mizzen said.
"The involvement of H1 phosphorylation in controlling ribosomal RNA gene transcription had not been suspected at all previously," Mizzen said. "That was a totally novel finding of our work."
Further experiments revealed that hormone treatments (in this case estradiol and glucocorticoid), stimulate the association of phosphorylated H1 histones with the regulatory regions of hormone-responsive genes.
The new findings could lead to a better understanding of alterations to the cell cycle associated wit
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign