Histone H4 and H2B genes in rainbow trout (Salmo gairdnerii).

The complete nucleotide sequence of the 3.0-kb BamH I-Sst I restriction fragment contained within the rainbow trout genomic clone lambda TH2 has been determined. This region contains the rainbow trout H4 and H2B histone genes and 5' and 3' flanking and spacer sequences, and represents the 5' half of the histone-gene cluster; the remaining half has been characterized previously. The genes are uninterrupted, and are transcribed from the same strand. The protein sequence of H4, as determined from the nucleic acid sequence, is the same as that derived for other vertebrate H4 proteins, although comparison of nucleotide sequences shows a great deal of sequence divergence, especially in the third base position. The amino acid sequence of H2B, though largely homologous to those of other vertebrate H2B proteins, displays some characteristic differences in primary structure. Consensus sequences noted in many other eukaryotic genes, as well as histone-specific consensus sequences, have been identified. An unusual feature of the spacer region between the H4 and H2B genes is the presence of a duplicated sequence 87 bp in length. The 5' and 3' ends of each repeat are complementary, and each repeat contains smaller repeated sequences internally, as well as a possible cruciform structure.