Organization and nucleotide sequence of the cluster of five histone genes in the polichaete worm Chaetopterus variopedatus: First record of a H1 histone gene in the phylum Annelida

Histone genes were identified and their nucleotide sequences were determined in the polychaete marine worm Chaetopterus variopedatus. The genes are organized in about 390 clusters of 7.3 kbp. Each cluster contains one copy of the five histone genes. The H1 histone gene present in the clusters is the first ever isolated in the phylum Annelida. The cluster has the unique peculiarity that all genes contain both the replication-dependent and the replication-independent 3' mRNA termination signals. Despite the differences in cluster organization and transcription polarity of the individual histone genes between C. variopedatus and Platynereis dumerilii, the other annelid in which histone genes have been studied, phylogenetic analysis of the encoded amino acid sequences clearly groups together those two organisms in a tree in which the other studied worms find closely related positions on the same evolutionary branch.