Testis-specific chromatin protein that specifically binds histone H4 acetylated at 'Lys-5' and 'Lys-8' (H4K5ac and H4K8ac, respectively) and plays a key role in spermatogenesis. Required in late pachytene spermatocytes: plays a role in meiotic and post-meiotic cells by binding to acetylated histones at the promoter of specific meiotic and post-meiotic genes, facilitating their activation at the appropriate time. In the post-meiotic phase of spermatogenesis, binds to hyperacetylated histones and participates in their general removal from DNA. Also recognizes and binds a subset of butyrylated histones: able to bind histone H4 butyrylated at 'Lys-8' (H4K8ac), while it is not able to bind H4 butyrylated at 'Lys-5' (H4K5ac). Also acts as a component of the splicing machinery in pachytene spermatocytes and round spermatids and participates in 3'-UTR truncation of specific mRNAs in post-meiotic spermatids. Required for chromocenter organization, a structure comprised of peri-centromeric heterochromatin. Interacts with SMARCE1 (By similarity). Interacts with mRNA splicing machinery proteins SRSF2, DDX5, HNRNPK and TARDBP. Interacts with the acetylated N-terminus of histone H1, H2, H3 and H4. Interacts with P-TEFb components CDK9 and CCNT1/cyclin-T1 (By similarity). Detected on chromatin. Excluded from the chromocenter. Bromo domains mediate interaction with histones that have acetylated lysine residues at specific positions. Bromo domain 1 mediates binding with histone H4 acetylated at 'Lys-5' and 'Lys-8' (H4K5ac and H4K8ac, respectively). The bromo domains also recognize and bind a subset of butyrylated histones: able to bind histone H4 butyrylated at 'Lys-8' (H4K8ac), while it is not able to bind H4 butyrylated at 'Lys-5' (H4K5ac).