EFFECT OF ARTIFICIALLY INSERTED INTRON ON GENE-EXPRESSION IN SACCHAROMYCES-CEREVISIAE

The intron of the yeast RP51A gene was cloned with precision using the polymerase chain reaction (PCR) amplification method, and then insert ed into several different positions of the yeast URA3 gene as well as the PGK-lacZ fusion gene without introduction of additional exon seque nces. Analysis of transcripts of these genes showed that an intron ins erted near the transcription start site of the gene was spliced out ef ficiently, whereas the same intron sequences inserted 200 hp or furthe r downstream of the start site were not, resulting in a reduced level of mRNA. These results explain why intron-containing genes in yeast us ually have an intron near the 5' end.