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 inserted into several different positions of the yeast URA3 gene as well as the PGK-lacZ fusion gene without introduction of additional exon sequences. Analysis of transcripts of these genes showed that an intron inserted near the transcription start site of the gene was spliced out efficiently, whereas the same intron sequences inserted 200 bp or further downstream of the start site were not, resulting in a reduced level of mRNA. These results explain why intron-containing genes in yeast usually have an intron near the 5' end.