Abstract
Histone 4 replacement (H4r) can replace replication-dependent H4 in Drosophila. To study the evolution of epigenetic mechanisms, the H4 and H4r genes from 14 Drosophila species were compared with regard to gene arrangement, codon bias and flanking sequences. Although the amino acid sequences of H4 and H4r are identical or nearly identical, the gene structures are quite different. The H4r gene is a single copy gene located 3R88C9 in D. melanogaster between punt and CEP78K, as it is in 11 closely related Drosophila species, but not in the three distantly related species. The H4r gene, unlike the H4 gene, has two introns and generates polyadenylated transcripts. The codon usage bias at particular sites differed between H4r and H4. The H4r gene had more GC pairs at 3rd codon position. Strongly conserved signal sequence was not found in the 5’-region or 3’-region of the H4r gene. These results suggested that the post transcriptional process such as modifying histone at or after translation will be important for replacing histones and remodeling the chromatin. The evolutionary changes that affect gene structure and codon usage might be a key step to develop epigenetic systems by replacement histones.
Highlights
Knowledge about histone variants and histone modifications has become very important for studying topics in cell biology such as gene expression, DNA replication, development, cell memory, and chromatin remodeling [1,2,3]
For 11 of the 14 species, the Histone 4 replacement (H4r) gene was located between a punt gene and a Cep78K gene
The spacer between punt and the H4r gene was only slightly longer in D. pseudoobscura and D. persimilis than in the other eight, but it was much longer in D. willistoni
Summary
Knowledge about histone variants and histone modifications has become very important for studying topics in cell biology such as gene expression, DNA replication, development, cell memory, and chromatin remodeling [1,2,3]. A replacement H4 (H4r) that replaces H4 has been reported [15] These two types of histone 4, H4 and H4r, have identical amino acid sequences [15]. This is probably because the H4 is highly conservative and even a single amino acid substitution was not permitted during the evolution of the two types. This identity is why H4r is called a replacement histone not a histone variant
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