Chioda M, Eskeland R, Thompson EM.

Mol Biol Evol. 2002 Dec;19(12):2247-60 doi:10.1093/oxfordjournals.molbev.a004048

Histone gene complement, variant expression, and mRNA processing in a urochordate Oikopleura dioica that undergoes extensive polyploidization.

• Oikopleura dioica H3.1 gene, H4.1 gene, H1.1 gene, and H2A.1 gene
• Oikopleura dioica H2A.3 gene for histone h2A.3
• Oikopleura dioica H3.2 gene for histone h3.2
• Oikopleura dioica partial H2A.2 gene for histone h2A.2
• Oikopleura dioica partial H2A.4 gene for histone H2A.4
• Oikopleura dioica mRNA for histone H2A.1a (H2A.1a gene)
• Oikopleura dioica partial mRNA for histone h2A.1b (H2a.1b gene)
• Oikopleura dioica partial mRNA for histone h4 (H4 gene)
• Oikopleura dioica partial mRNA for histone h1.2 (H1.2 gene)

“Densitometric analyses of Southern blots yielded estimates of 9–11 H4 genes, 11–14 H3 genes, 15–19 H2A genes, 18–20 H2B genes, and 4–7 H1 genes.” “The quintet cluster consisted of a central H1 gene flanked by divergently transcribed H3-H4 and H2A-H2B pairs, an organization found in other organisms such as humans. The quintet cluster is extremely compact, covering only 3.5 kb.” “Both visual inspection and PRATT analysis (Jonassen 1997 ) of the sequences 3′ to the conserved stem-loop revealed no consensus 3′ purine-rich histone downstream element (HDE) that interacts with U7 snRNA in the processing of histone mRNAs. In fact, no consensus sequence or pattern motif of any kind was discovered 3′ of the stem-loop in O. dioica histone gene sequences.”