PT - JOURNAL ARTICLE AU - Flanagan, Thomas W. AU - Files, Jacob K. AU - Casano, Kelsey Rose AU - George, Eric M. AU - Brown, David T. TI - Photobleaching studies reveal that a single amino acid polymorphism is responsible for the differential binding affinities of linker histone subtypes H1.1 and H1.5 AID - 10.1242/bio.016733 DP - 2016 Mar 15 TA - Biology Open PG - 372--380 VI - 5 IP - 3 4099 - http://bio.biologists.org/content/5/3/372.short 4100 - http://bio.biologists.org/content/5/3/372.full SO - Biology Open2016 Mar 15; 5 AB - Mammals express six major somatic linker histone subtypes, all of which display dynamic binding to chromatin, characterized by transient binding at a given location followed by rapid translocation to a new site. Using photobleaching techniques, we systematically measured the exchange rate of all six mouse H1 subtypes to determine their relative chromatin-binding affinity. Two subtypes, H1.1 and H1.2, display binding affinities that are significantly lower than all other subtypes. Using in vitro mutagenesis, the differences in chromatin-binding affinities between H1.1 (lower binding affinity) and H1.5 (higher binding affinity) were mapped to a single amino acid polymorphism near the junction of the globular and C-terminal domains. Overexpression of H1.5 in density arrested fibroblasts did not affect cell cycle progression after release. By contrast, overexpression of H1.1 resulted in a more rapid progression through G1/S relative to control cells. These results provide structural insights into the proposed functional significance of linker histone heterogeneity.