Transition Protein 1 (TNP1)

Transition protein-1 is a spermatid-specific product of the haploid genome which replaces histone and is itself replaced in the mature sperm by the protamines. Yu et al. (2000) generated mice lacking the major transition nuclear protein, TP1, by targeted deletion of the Tnp1 gene in mouse embryonic stem cells. Surprisingly, testis weights and sperm production were normal in the mutant mice, and only subtle abnormalities were detected in sperm morphology.

Electron microscopy showed large rod-like structures in the chromatin of mutant step 13 spermatids, in contrast to the fine chromatin fibrils observed in wildtype. Steps 12-13 spermatid nuclei from the testis of Tnp1-null mice contained, in place of TP1, elevated levels of TP2 (TNP2) and some PRM2 precursor.