PRM1 (protamine 1) is a sperm-specific histone substitute that plays a critical role in male fertility. During spermiogenesis, PRM1 is expressed postmeiotically in round and elongating spermatids 1 where it functions alongside PRM2 and transition proteins to compact and condense DNA into highly stable, transcriptionally inactive chr16 2. The PRM1:PRM2 ratio must be precisely maintained (approximately 1:2 in wild-type) for proper sperm chr16 hypercondensation; disruption of this ratio leads to subfertility or infertility 2. PRM1 is semen-specific and serves as a reliable biomarker for forensic body fluid identification 3. At fertilization, SRPK1-catalyzed phosphorylation of PRM1 initiates protamine-to-histone exchange in the oocyte, triggering parental genome reprogramming essential for embryonic development 4. Genetic variations in PRM1, particularly the rs2301365 polymorphism, are associated with increased male infertility risk 5. Notably, even a single amino acid substitution outside the arginine-rich core (K49A) significantly reduces protamine-DNA binding, alters sperm motility, and compromises male fertility and embryonic development 6. Beyond reproduction, PRM1 is identified as a cancer-testis antigen with potential applications in cancer immunotherapy and drug delivery systems 7.