The linker or H1 histone is a protein that binds and compacts DNA.  Recent investigations have shown that these histones are mobile proteins, constantly moving from one strand of DNA to another.  This movement of the H1 histone is thought to regulate chromatin compaction.  In this experiment, the mobility of different linker histone subtypes (H1a, H1b, H1c, and H1d) was measured and compared to the control (H10).  To achieve this purpose, DNA plasmids were created that were contained two different H1 protein genes, each attached to a different fluorescent protein.  These plasmids were introduced into mouse fibroblast cells and the cells produced the different histone subtypes that were coded for on the plasmid.  The mobility of each histone subtype was determined using a method called FRAP (Fluorescent Recovery After Photobleaching).  The results showed that this experimental system is superior to other methods and that there are significant differences among these subtypes with respect to their affinity to chromatin.  In addition, chromatin de-compaction, which is dependent upon H1 mobility, is necessary for efficient DNA repair.  Some radiation-resistant tumors have elevated levels of proteins that promote H1 mobility, therefore producing hyperactive DNA repair systems.  The information and techniques developed in this experiment will be useful for understanding this phenomenon in greater detail and might provide clues for effective treatments of these radiation-resistant tumors.

Quantitative analysis of the binding of mammalian linker histone isotopes to chromatin in vivo

245th National Meeting (2013)

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