COMPARISON OF 3 3'-NONCODING REGIONS IN SCHIZOSACCHAROMYCES-POMBE EXPRESSION VECTORS - EFFICIENCIES OF TRANSCRIPTION TERMINATION AND MESSENGER-RNA 3'-END FORMATION

Analysis of an established Schizosaccharomyces pombe episomal shuttle vector suggested that inefficient transcription termination was delete rious to plasmid function. We undertook a study to determine if transc ription in the presence and absence of 3'-processing within a vector c ould affect the ability of the plasmid to transform, transcribe and tr anslate the RNA produced. This report provides an analysis of the effe cts that three S. pombe 3'non-coding regions have on the transformatio n and expression efficiencies of a fission yeast plasmid vector. The 3 'regions from adh1, act1 and ura4 were tested for their ability to ter minate and process adh1 promoter-driven transcription of a lacZ report er gene. Differences between the 3'-processing sequences were observed , with transcription termination mediated by the ura4 3'region being m ore efficient than termination by the 3'regions of adh1 and act1. We s how that plasmids containing inefficient transcription termination sig nals result in readthrough transcription and reduced transformation ef ficiencies. In addition, the readthrough transcripts containing 3'non- coding regions show impaired translation efficiencies. We describe an S. pombe vector (pURAS) with a high transformation efficiency that dir ects the production of highly translatable, discrete-sized transcripts .