Sequence and transcript analysis of macronuclear histone H2B genes from Euplotes crassus

Area of Science:

• Molecular Biology
• Genetics
• Protozoology

Background:

• The ciliated protozoan Euplotes crassus possesses macronuclear chromosomes containing histone genes.
• Histone H2B proteins are crucial for nucleosome structure and DNA regulation across eukaryotes.

Purpose of the Study:

• To clone and sequence histone H2B genes from Euplotes crassus macronuclear chromosomes.
• To analyze the structure, expression, and regulation of these histone H2B genes.

Main Methods:

• Macronuclear chromosome cloning and DNA sequencing.
• Primer extension assays to determine transcription start sites.
• Northern blot analysis for mRNA abundance during the sexual cycle.
• 3' RACE (Rapid Amplification of cDNA Ends) for coexpression analysis.

Main Results:

• Two distinct 1.5-kb macronuclear chromosomes carrying histone H2B genes were identified and sequenced.
• The genes encode an identical 113-amino acid histone H2B protein with a truncated N-terminus and conserved C-terminus.
• Histone H2B mRNA levels fluctuate with DNA replication during the sexual phase.
• Analysis indicates that the histone H2B genes are coexpressed.

Conclusions:

• Euplotes crassus histone H2B genes exhibit conserved protein structure despite significant divergence in noncoding regions.
• The regulation of histone H2B gene expression is linked to DNA replication dynamics within the sexual cycle of this ciliate.