Testis-specific serine/threonine-protein kinase required during spermatid development. Phosphorylates 'Ser-288' of TSKS. Involved in the late stages of spermatogenesis, during the reconstruction of the cytoplasm. During spermatogenesis, required for the transformation of a ring-shaped structure around the base of the flagellum originating from the chromatoid body (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with TSSK2. Interacts with HSP90; this interaction stabilizes TSSK1. In spermatozoa, present in the sperm head and in the flagellum. Autophosphorylated. Ubiquitinated; HSP90 activity negatively regulates ubiquitination and degradation. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family.