Regulation of Histone H3 Proteolysis by Acetylation in Tetrahymena thermophila

• Main Author: Sherman, Robyn
• Format: Others
• Published: Scholarship @ Claremont 2015
• Subjects: Tetrahymena; clipping; histone H3; acetylation; Biology; Life Sciences; Molecular Biology
• Online Access: http://scholarship.claremont.edu/scripps_theses/598; http://scholarship.claremont.edu/cgi/viewcontent.cgi?article=1538&context=scripps_theses

Chromatin is the combination of DNA and proteins in the nucleus that is used to aid in the compaction of DNA. Histones are a group of proteins used to condense DNA by forming a complex (nucleosome) around which DNA wraps around; there are two of each type of histone in a nucleosome: H2A, H2B, H3 and H4. Once the DNA is wrapped around the histones, the genome is further compacted. A shortened, "clipped" version of histone H3 has been found in some organisms including yeasts, flies, mammalian stem cells, and the ciliated protozoan, Tetrahymena thermophila. In each organism, clipping occurs at a different site on the N-terminus, usually before an alanine residue. Clipping is important as it may affect other epigenetic modifications and gene regulation in cell differentiation, but the regulation of this histone proteolysis has remained largely unstudied. In Tetrahymena thermophila, approximately half of the histone H3 molecules are clipped between residues 6 and 7 on histone H3, solely in the transcriptionally silent micronucleus. The histones in the micronuclei are deacetylated, while histones in the macronuclei can be acetylated or deacetylated. It is hypothesized that the post-translational acetylation modification to the histone tails may inhibit histone H3 clipping. Immunoblot analyses were carried out with acetylated and deacetylated micronuclei, demonstrating an increase of clipping when acetylated. Additionally, mutations were created at lysine 9 upstream of the clip site on the histone H3 tails to mimic acetylation and deacetylation to study whether the modification of that site has a regulatory effect.