The authors describe a method for synthesizing microgram quantities of eukaryotic messenger RNAs (mRNAs) using SP6 in vitro transcription of cloned cDNAs. They demonstrate that these synthetic RNAs function efficiently as mRNAs when injected into frog oocytes or added to wheat germ extracts. The study confirms that a 5' cap on the mRNA is essential for translation in injected oocytes and shows that most of the 3' flanking region, including the poly A tail, can be deleted without abolishing protein synthesis. The method involves in vitro transcription of cDNAs cloned into SP6 vectors, allowing the production of large amounts of mRNA and subsequent protein synthesis. This approach enables the analysis of the significance of specific structural features of mRNAs without resorting to conventional genetic methods. The results highlight the stability and translational efficiency of synthetic mRNAs, providing a valuable tool for studying mRNA function and protein synthesis.The authors describe a method for synthesizing microgram quantities of eukaryotic messenger RNAs (mRNAs) using SP6 in vitro transcription of cloned cDNAs. They demonstrate that these synthetic RNAs function efficiently as mRNAs when injected into frog oocytes or added to wheat germ extracts. The study confirms that a 5' cap on the mRNA is essential for translation in injected oocytes and shows that most of the 3' flanking region, including the poly A tail, can be deleted without abolishing protein synthesis. The method involves in vitro transcription of cDNAs cloned into SP6 vectors, allowing the production of large amounts of mRNA and subsequent protein synthesis. This approach enables the analysis of the significance of specific structural features of mRNAs without resorting to conventional genetic methods. The results highlight the stability and translational efficiency of synthetic mRNAs, providing a valuable tool for studying mRNA function and protein synthesis.