Histone H2B genes of yeast encode two different proteins

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Histones are crucial proteins for DNA packaging in eukaryotes.
• Histone H2B is a core component of the nucleosome.
• Understanding histone gene evolution provides insights into chromatin structure and function.

Purpose of the Study:

• To sequence and analyze two unlinked histone H2B genes from Saccharomyces cerevisiae.
• To compare the deduced H2B protein sequences with those of higher eukaryotes.
• To investigate the evolutionary relationship between the two yeast H2B genes.

Main Methods:

• Gene sequencing of Saccharomyces cerevisiae histone H2B.
• Amino acid sequence comparison of H2B proteins.
• DNA sequence analysis, including prelude and coding regions.
• Estimation of gene duplication events based on sequence divergence.

Main Results:

• Two distinct, unlinked histone H2B genes were identified in Saccharomyces cerevisiae.
• The encoded H2B proteins differ by only 4 amino acids out of 130.
• High homology was observed between yeast and higher eukaryote H2B proteins, particularly at the carboxyl terminus.
• Extensive base substitutions were found between the two yeast H2B genes, with 12.6% divergence in coding regions and 64% in prelude sequences.
• The divergence suggests the genes resulted from an ancient duplication event.

Conclusions:

• The two Saccharomyces cerevisiae histone H2B genes are likely products of an ancient duplication.
• Despite DNA sequence divergence, the H2B protein structure is highly conserved, especially in critical functional regions.
• Comparative analysis highlights conserved and divergent evolutionary paths of histone genes across eukaryotes.