Effect of transfer RNA from various sources on placental messenger RNA translation

Poly(A+)-containing mRNA from human term placenta was used to direct protein synthesis in a nuclease-treated rabbit reticulocyte lysate, which is dependent on mRNA and tRNA for maximal activity. The major protein product was human pre-placental lactogen (hPL). Addition of tRNA from rabbit liver, rabbit reticulocyte, human first trimester and term placenta, human liver and yeast resulted in 2-5-fold stimulation of [35S]methionine incorporation into total protein. Although all mammalian tRNA increased hPL synthesis, the relative synthesis as compared to endogenous globin was markedly different and most efficient with tRNA from term placenta. Addition of yeast tRNA increased total incorporation 3-fold but decreased incorporation of [35S]methionine into pre-hPL. These results suggest that the population of isoacceptor tRNAs may influence the expression of hPL in term placenta. Results are discussed by showing codon bias and usage of mRNA coding for hPL, alpha- and beta-hCG, rabbit globin and yeast alcohol dehydrogenase I.