Mytilus edulis histone gene clusters containing only H1 genes

We isolated five different phage clones containing histone gene clusters wi th up to five H1 genes per phage clone from a Mytilus edulis genomic librar y. Among these Ill genes, nine gene types coding for five different H1 prot eins have been identified. All H1 histone genes were located on repetitive restriction fragments with only slightly different sizes. The H1 coding reg ions show highly related sequences, suggesting that the multitude of H1 gen es has evolved by gene duplication events. Core histone genes could not be found on these five Mytilus edulis genome fragments.