Sequence differences between histones of procyclic Trypanosoma brucei brucei and higher eukaryotes

Area of Science:

• Molecular Biology
• Parasitology
• Biochemistry

Background:

• Histones are crucial for DNA packaging in eukaryotes.
• Trypanosoma brucei brucei, a protozoan parasite, possesses unique genomic organization.
• Understanding T. b. brucei histones can reveal alternative genetic material processing.

Purpose of the Study:

• To isolate and characterize histones from procyclic Trypanosoma brucei brucei.
• To compare T. b. brucei histone sequences with those from other eukaryotes.
• To investigate the structural and functional implications of histone variations in T. b. brucei.

Main Methods:

• Isolation and purification of four histone proteins (a, b, c, d) from T. b. brucei.
• Enzymatic cleavage of histones using Endoproteinase Glu-C.
• Separation of peptide fragments via FPLC reversed-phase chromatography.
• Amino acid sequence analysis of selected histone fragments.

Main Results:

• Identified histone fragments with partial sequence identity to H2B and H4.
• Fragment a9 showed 54-57% identity to H3 sequences from other species.
• Significant sequence differences (21-48%) were observed between T. b. brucei histones and calf thymus histones.
• No alignment was found for fragments a5 and b6 with known eukaryotic histones.
• Lack of a functional histone H1 was noted.

Conclusions:

• T. b. brucei histones exhibit unique sequence patterns distinct from higher eukaryotes.
• These differences likely impact histone-histone and histone-DNA interactions within the nucleosome.
• The absence of a 30 nm fiber formation is potentially linked to these histone variations and lack of H1.
• Alternative nucleosome organization in T. b. brucei may have chemotherapeutic implications.