Isolation and characterization of the gene encoding the testis specific histone protein H2B-2 from the sea urchin Lytechinus pictus. We have cloned and characterized the gene encoding a sperm specific H2B-2 histone subtype from the sea urchin L. pictus. The gene is not clustered with any other histone genes. However, it resembles other histone genes in many respects. The gene contains no intervening sequences or polyadenylation signals. Like other histone genes it contains the conserved 3'' hairpin loop sequence and CAAGAAAGA box necessary for the processing of the 3'' end of the histone transcript. Upstream of the gene in addition to the TATA box, and two copies of inverted CCAAT Boxes is a conserved sequence element found in many H2B genes. Unlike most histone genes, the H2B-2 gene is expressed in a sex and tissue specific manner only in testis. The sperm H2B-2 subtype encoded by this gene is 142 amino acids in length. The larger size of this H2B protein is accounted for by residues in the N-terminus of the protein consisting of a series of pentapeptide repeats typical of this histone subtype.