Isolation of two clusters of mouse histone genes

Histone mRNA was partially purified from mouse myeloma cells synchronized in S phase by isoleucine starvation. A cDNA was prepared that contained sequences complementary to all five mouse histone genes. This cDNA was used to screen a library of mouse DNA in lambda phage. The positive clones were screened by hybridization with sea urchin histone gene-specific probes to identify those clones that contained histone genes. Confirmation of this identification was obtained by hybridization with Drosophila histone genes. Two independent clusters of histone genes were isolated. One, MM531, contains regions hybridizing specifically to H3, H4, and H1 and the other, MM221, contains two regions hybridizing specifically to H3 and single regions complementary to H4, H2b, and H2a. They are not part of a simple repeating structure. The nucleotide sequence of the coding region of the H3 gene in MM531 has been determined. This gene could code for a variant H3 protein that has several amino acid substitutions not reported in other H3 proteins.