Differential expression of two clusters of mouse histone genes

The mouse histone mRNAs coded for by three different cloned DNA fragments have been characterized. Two of these cloned DNA fragments, MM221 and MM291, located on chromosome 13, code for H3, H2b and H2a histone mRNAs, which are expressed at low levels in cultured mouse cells and fetal mice. The other DNA fragment, MM614, located on chromosome 3, codes for an H3 and an H2a mRNA, which are expressed at high levels in these cells. The mRNAs for each histone protein share common coding region sequences, while the untranslated regions of all the genes have diverged significantly, as judged by S1 nuclease mapping. Amino acid substitutions in some H3, H2a and H2b proteins are detected as internal cleavages in the S1 nuclease maps. All of these genes code for replication variant histone mRNAs, which are regulated in parallel with DNA synthesis.