Extremely divergent histone H 4 sequence from trypanosoma cruzi : Evolutionary implications

Trypanosoma cruzi presents six histones electrophoretically resolved in three gel systems. Indirect evidence shows that one of these histones, name, corresponds to H 4 in other species. We present evidence that histones is H 4 by sequencing its amino terminal end. The amino terminal of T. cruzi histone H 4 , unlike that of other H 4 s examined thus far is not blocked. Moreover, this protein presents two variants. This partial amino acid sequence of T. cruzi histone H 4 differs greatly from homologous sequences of human, yeast, or Tetrahymena . Since the conservatism of the core histones (H 2 A, H 2 B, H 3 , and H 4 ) is clearly illustrated by comparative sequence analyses, the data shown here demonstrates that T. cruzi histone H 4 is the most divergent reported. Quantitative analysis of the data suggests that the rate of substitutions in the histone H 4 amino terminal sequence varies among different lineages. We postulate a slow‐down in the evolutionary rate of histone H 4 amino terminal domain in the metazoa branch related perhaps to the appearance of a novel function for this domain.