Sequences of four mouse histone H3 genes: implications for evolution of mouse histone genes

The sequences of four histone H3 genes coding for the replication variant proteins H3.1 and H3.2 have been determined. Three of these genes, two coding for H3.1 proteins and one for an H3.2 protein, are located on chromosome 13 and expressed at low levels. The fourth gene, encoding an H3.2 protein, is located on chromosome 3 and expressed at a high level. The coding regions of the three genes on chromosome 13 are more similar to each other than to the H3 gene on chromosome 3, and equally divergent from it, suggesting that either gene duplication or gene conversion has occurred since the genes were dispersed onto two chromosomes. A 14-base sequence including the CCAAT sequence and located 5' to the genes on chromosome 13 has been conserved. The histone H3 gene on chromosome 3 has multiple potential binding sites for the Sp1 transcription factor. The coding regions show greater than 95% conservation among the four genes. This is due to the strict pattern of codon usage and the presence of two long (greater than 60 base) regions of completely conserved nucleic acid sequence. These conserved regions in the coding sequence may have an important functional role at the mRNA or DNA level.