This study describes a method for synthesizing functional messenger RNAs (mRNAs) using in vitro transcription of cloned cDNAs with SP6 RNA polymerase. The synthesized mRNAs are efficiently translated in frog oocytes and wheat germ extracts. The 5' cap is essential for translation in injected oocytes, while most of the 3' flanking region, including the poly A tail, can be removed without affecting protein synthesis. The method allows for the production of large amounts of functional mRNAs from any cDNA clone. The SP6 in vitro transcription system produces mRNAs that closely resemble authentic mRNAs, including the 5' cap and 3' poly A tail. The study also shows that synthetic mRNAs can be used to direct the synthesis of proteins in injected oocytes and in wheat germ extracts. The results demonstrate that hybrid mRNAs produced with the SP64T vector are translated in injected oocytes, establishing a general method for producing large amounts of any messenger RNA if the protein coding region of a gene has been cloned. The study also shows that synthetic mRNAs can be used to direct the synthesis of proteins in injected oocytes and in wheat germ extracts. The results indicate that the 5' cap is essential for mRNA stability in injected oocytes, while the 3' flanking region is not absolutely required for protein synthesis. The study also shows that synthetic mRNAs can be used to direct the synthesis of proteins in injected oocytes and in wheat germ extracts. The results suggest that the 5' untranslated region can be altered without affecting mRNA function. The study also shows that the 3' flanking region is not absolutely required for protein synthesis. The results indicate that the poly A tail is essential for the functional stability of mRNAs in injected oocytes, but not for experiments in which protein synthesis is assayed in shorter periods. The study concludes that the SP6 RNA polymerase system is a convenient and efficient method for producing functional mRNAs.This study describes a method for synthesizing functional messenger RNAs (mRNAs) using in vitro transcription of cloned cDNAs with SP6 RNA polymerase. The synthesized mRNAs are efficiently translated in frog oocytes and wheat germ extracts. The 5' cap is essential for translation in injected oocytes, while most of the 3' flanking region, including the poly A tail, can be removed without affecting protein synthesis. The method allows for the production of large amounts of functional mRNAs from any cDNA clone. The SP6 in vitro transcription system produces mRNAs that closely resemble authentic mRNAs, including the 5' cap and 3' poly A tail. The study also shows that synthetic mRNAs can be used to direct the synthesis of proteins in injected oocytes and in wheat germ extracts. The results demonstrate that hybrid mRNAs produced with the SP64T vector are translated in injected oocytes, establishing a general method for producing large amounts of any messenger RNA if the protein coding region of a gene has been cloned. The study also shows that synthetic mRNAs can be used to direct the synthesis of proteins in injected oocytes and in wheat germ extracts. The results indicate that the 5' cap is essential for mRNA stability in injected oocytes, while the 3' flanking region is not absolutely required for protein synthesis. The study also shows that synthetic mRNAs can be used to direct the synthesis of proteins in injected oocytes and in wheat germ extracts. The results suggest that the 5' untranslated region can be altered without affecting mRNA function. The study also shows that the 3' flanking region is not absolutely required for protein synthesis. The results indicate that the poly A tail is essential for the functional stability of mRNAs in injected oocytes, but not for experiments in which protein synthesis is assayed in shorter periods. The study concludes that the SP6 RNA polymerase system is a convenient and efficient method for producing functional mRNAs.