Histone gene organization of fission yeast: a common upstream sequence

Histone genes of the fission yeast Schizosaccharomyces pombe were cloned from Charon 4A and cosmid gene libraries by hybridization, and their nucleotide sequences were determined. The genome of S. pombe has a single, isolated H2A, a pair of H2A-H2B and three pairs of H3-H4 (one H2B, two H2A and three each of H3 and H4). This non-assorted histone gene organization is distinct from that of the budding yeast which has two pairs of H2A-H2B and H3-H4. The predicted amino acid sequences of S. pombe histone H2As, H3s and H4s were identical except for three residue changes in H2As. Compared with those os S. cerevisiae and human, variable residues were clustered near the NH2- and COOH-terminal regions of H2A and H2B. Sequence homologies to the two organisms were roughly the same in H2A (79-83%), H3 (92-93%) and H4 (91%), but differed in H2B (82% to S. cerevisiae and 68% to human). The coding sequences in pairs of S. pombe histone genes were divergently directed. A 17-bp long highly homologous sequence (AACCCT box) that had internal 6-bp direct repeats was present in the intergene spacer sequences or in the 5' upstream region of all the cloned histone genes. A possible regulatory role of the common upstream sequence for histone gene expression is discussed.