Activation of transcription of a yeast gene in E. coli by an IS5 element.

Abstract

pRG4 and pRG5 are two plasmids derived1 from pBR322 which carry an integrated yeast DNA segment (2.5 kilobases) containing the URA1 gene2,3 and differ only in the orientation of the insert. Escherichia coli pyrD cells transformed by pRG4 recover the ability to grow on minimal medium whereas pRG5-transformed pyrD cells do not3. The spontaneous integration of an insertion (IS) element into the cloned DNA segment corrects the absence of complementation in pRGS-transformed pyrD cells3. The new plasmid resulting from such an insertion event has been named pRG7 (Fig. 1). To determine the level at which the IS element affected URA1 expression, we assayed the RNAs which hybridized to each strand of URA1 DNA in various transformed pyrD strains, using as a probe single-stranded URA1 DNA cloned in phage fd1064. The results showed that the switching on of yeast gene by the IS element occurred at the transcriptional level, strongly suggesting that this IS element can serve as a mobile promoter in E. coli. The IS element has been identified as an IS5.