RNA turnover and protein synthesis in fish cells

Protein synthesis in fish has been previously correlated with RNA content. The present study investigates whether protein and RNA synthesis rates are similarly related. Protein and RNA synthesis rates were determined from H-3 -phenylalanine and H-3-uridine incorporation, respectively, and expressed a s % . day(-1) and half-lives, respectively. Three fibroblast cell lines wer e used: BF-2, RTP, CHSE 214, which are derived from the bluegill, rainbow t rout and Chinook salmon, respectively. These cells contained similar RNA co ncentrations (similar to 175 mu g RNA.mg(-1) cell protein). Therefore diffe rences in protein synthesis rates, BF-2 (31.3 +/- 1.8) > RTP (25.1 +/- 1.7) > CHSE 214 (17.6 +/- 1.1), were attributable to RNA translational efficien cy. The most translationally efficient RNA (BF-2 cells), 1.8 mg protein syn thesised . mu g(-1) RNA . day(-1), corresponded to the lowest RNA half-life , 75.4 +/- 6.4 h. Translationally efficient RNA was also energetically effi cient with BF-2 cells exploiting the least costly route of nucleotide suppl y (i.e. exogenous salvage) 3.5 -6.0 times more than the least translational ly efficient RNA (CHSE 214 cells). These data suggest that differential nuc leotide supply, between intracellular synthesis and exogenous salvage, cons titutes the al-ca of pre-translational flexibility exploited to maintain RN A synthesis as a fixed energetic cost component of protein synthesis.