Subunits of the Histone Chaperone CAF1 Also Mediate Assembly of Protamine-Based Chromatin

• CAF1 subunits mediate the assembly of two fundamentally different forms of chromatin
• CAF1-p180 and CAF1-p75 subunits have distinct functions during spermatogenesis
• CAF1-p180 and CAF1-p75 are required for protaminization of the paternal genome
• CAF1-p75 is a protamine-loading factor

SummaryOne of the most dramatic forms of chromatin reorganization occurs during spermatogenesis, when the paternal genome is repackaged from a nucleosomal to a protamine-based structure. We assessed the role of the canonical histone chaperone CAF1 in Drosophila spermatogenesis. In this process, CAF1 does not behave as a complex, but its subunits display distinct chromatin dynamics. During histone-to-protamine replacement, CAF1-p180 dissociates from the DNA while CAF1-p75 binds and stays on as a component of sperm chromatin. Association of CAF1-p75 with the paternal genome depends on CAF1-p180 and protamines. Conversely, CAF1-p75 binds protamines and is required for their incorporation into sperm chromatin. Histone removal, however, occurs independently of CAF1 or protamines. Thus, CAF1-p180 and CAF1-p75 function in a temporal hierarchy during sperm chromatin assembly, with CAF1-p75 acting as a protamine-loading factor. These results show that CAF1 subunits mediate the assembly of two fundamentally different forms of chromatin.

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