Sin mutations of histone H3: influence on nucleosome core structure and function

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• SWI/SNF complex is crucial for yeast transcription.
• Sin mutations in Saccharomyces cerevisiae bypass SWI/SNF defects.
• Histone H3 mutations are investigated for their role in the Sin phenotype.

Purpose of the Study:

• To investigate the structural and functional consequences of Sin mutations in histone H3 on nucleosome stability.
• To test if Sin mutations lead to nucleosomal destabilization.
• To understand how altered nucleosome structure affects DNA binding proteins.

Main Methods:

• Topoisomerase I-mediated relaxation of minichromosomes.
• Micrococcal nuclease digestion to assess DNA accessibility.
• DNase I digestion to analyze DNA rotational positioning.
• Assessing binding of TATA-binding protein/transcription factor IIA and RNA polymerase III.

Main Results:

• Certain Sin mutations in histone H3 (R116-H, T118-I) destabilize nucleosomes, increasing DNA accessibility and altering rotational positioning.
• Other Sin mutations (E105-K) show minimal changes in nucleosome structure and stability.
• Both mutant and wild-type nucleosomes restrict binding of transcription machinery.
• Nucleosomal destabilization is not a universal outcome of Sin mutations.

Conclusions:

• Sin mutations in histone H3 impact histone-DNA interactions to varying degrees.
• Destabilization of nucleosomes is not always required for the Sin phenotype.
• The fundamental nucleosome architecture is maintained despite alterations in histone-DNA contacts.
• Sin mutations contribute to a common phenotype through diverse effects on nucleosome stability.