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Trout Testis Cells

II. SYNTHESIS AND PHOSPHORYLATION OF HISTONES AND PROTAMINES IN DIFFERENT CELL TYPES

From the ¹ From the Department of Biochemistry, The University of British Columbia, Vancouver 8, British Columbia, Canada

Trout testis cells were labeled with [³H]arginine or lysine and inorganic [³²P]phosphate. Cells at different stages of spermatogenesis were separated by their differing velocities of sedimentation in serum albumin gradients at one gravity. The basic proteins from each of these cell types were separated and analyzed for radioactivity in starch gels. Most of the histones were synthesized and phosphorylated in diploid cells of sedimentation velocity 2.8 and 3.5; very little synthesis or phosphorylation of histone occurred in the spermatids. Although different rates of histone synthesis and phosphorylation were found in different cell types, the ratios of synthesis to phosphorylation were close to unity in each case. The positive correlation between these and the rates of DNA synthesis suggest that the phosphorylation of histone may be required for the correct binding of histone to DNA. The half-life of phosphate in histones varied from 8 to 13 hours in cells actively synthesizing histones but was very long in protamine stage spermatids. In addition, labeled arginine did not appear in unmodified histone IV until 21 hours after the start of the incorporation suggesting that newly synthesized histone IV may pass through a series of modifications before reaching its final unmodified state.

Protamine synthesis begins in spermatid cells at a middle stage of spermiogenesis and the newly synthesized protamine is extensively phosphorylated. The cellular specificity of histone phosphorylation suggests that this process is not required for the progressive loss of histones during the transition of spermatids sedimenting at 1.5 mm per hour to spermatids sedimenting at 1.0 mm per hour.

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