Characterization of a hemolytic protein, identified as histone H4, from the skin of the Japanese tree frog Hyla japonica (Hylidae)

An extract of the skin of the Japanese tree frog, Hyla japonica Günther, 1859 (Anura: Hylidae) did not inhibit the growth of the bacteria Escherichia coli or Staphylococcus aureus, but contained a protein that was strongly hemolytic against human erythrocytes. The protein was purified to near homogeneity by reverse-phase HPLC, and its N-terminal amino acid sequence (SGRGKGGKGL...) identified it as histone H4. The complete primary structure of the 102-amino-acid-residue histone H4 was determined by a combination of molecular cloning of genomic and complementary DNAs encoding the protein. The molecular mass of the purified histone H4 determined by electrospray mass spectrometry was 71 ± 2 Daltons greater than that predicted from the deduced amino acid sequence of the protein. The + 71 mass units is consistent with the proposal that the protein isolated from the skin was post-translationally modified by addition of one acetyl and two methyl groups. The stem-loop structure at the 3′ flanking region of the H. japonica histone H4 gene, which acts as a transcription termination signal, contained a nucleotide sequence (5′-GGCTCTCCTCAGAGCC-3′) with unusual structural features not seen in other histone genes.