The expression of barley α-amylase genes in Xenopus laevis oocytes

The synthesis and secretion of α-amylase (EC 3.2.1.1) from Xenopus laevis oocytes injected with plasmids containing barley α-amylase complementary DNA (cDNA), genomic DNA, or synthetic α-amylase mRNA were studied. α-Amylase accumulated within the oocytes beginning 12 h after injection of DNA and in the medium 12 h later as a result of secretion. S1 mapping showed that the transcription of genomic DNA was initiated at the same site in oocytes as in barley aleurone, but that the transcription of cDNAs was less precise than that of genomic DNA. The α-amylase secreted by oocytes injected with either RNA or DNA had a molecular mass (Mr) of 44000 daltons (Da) and was indistinguishable from native barley α-amylase in size, isoelectric point, antigenicity and enzymatic activity. Isoelectric focussing showed that two enzymatically active isoforms of α-amylase were synthesized and secreted from oocytes injected with synthetic RNA or DNA. The results permit us to assign specific electrophoretic bands to specific cDNA clones. We conclude that the Xenopus oocyte is a promising surrogate system for the study of transcription and translation of plant genes.