Analysis of the selenocysteine tRNA[Ser]Sec gene transcription in vitro using Xenopus oocyte extracts

An in vitro transcription system was devised using a Xenopus oocyte S150 extract for analyzing expression of the Sec tRNA[Ser]Sec gene. The activator element, located at about -200 that is required for maximal expression of the tRNA[Ser]Sec gene in vivo, had no effect on tRNA[Ser]Sec transcription in vitro. In vitro transcription of this gene even tolerated mutations within or deletion of the PSE, showing marked contrast with the requirements observed in vivo. However, the TATA box was indispensable for basal level expression of the gene both in vivo and in vitro. The region spanning from the TATA box to the transcription start point (-33 to -1) was sufficient for Pol III to recognize the tRNA[Ser]Sec gene promoter in vitro.