The mechanism by which body temperature inhibits protein biosynthesis in spermatids of rat testes

Spermatids prepared from rat testes showed lower incorporation of amino acids into protein when incubated at 37° than at 34°C; incubation at 40°C further decreased incorporation. Qualitatively similar results were obtained with spermatid lysate. Incubation at 37°C affected ribosomes but not supernatant. The proportion of ribosomes found in the polyribosomal fractions was less at 37° that at 34°C, whether the distribution was determined by A₂₅₄ or by radioactivity associated with nascent peptides. Chain elongation plus termination was not different at 34° and 37°C. Formation of the 40 S·tRNA·methionine complex was slower at 37° than at 34°C, although the complex once formed was equally stable at both temperatures. When initiation was inhibited by NaF, one round of translation resulted in the same production of radioactive peptide at both temperatures, whereas more rounds were completed in a given time at 34° as opposed to 37°C. Finally after incubation of spermatids with [³H]tyrosine at 37° and 34°C, electrophoresis on sodium dodecyl sulfate-polyacrylamide gels revealed that the lower production of tritiated peptides at 37° as opposed to 34°C was distributed throughout the gels, thus excluding the possibility that differences in the rates of synthesis of a few key proteins are responsible for the differences between protein synthesis at 34° and 37°C. It is concluded that differences between testicular protein synthesis at scrotal (34°C) and body (37°) temperatures are seen in purified fractions of immature spermatids and that at least part of the difference results from slower formation of the initiation complex 40 S·methionine·tRNA. tRNA.