DNA-binding protein that may be implicated in chromatin remodeling and/or transcriptional regulation during spermiogenesis, the process of spermatid maturation into spermatozoa. Expressed exclusively in the testis by haploid germ cells (at protein level). Expression initiated at step 9 of spermatid development and peaked between steps 10-13. Expression decreased abruptly at step 14 and was undetectable after step 15. Belongs to the histone H1/H5 family.