The simian virus 40 small-t intron, present in many common expression vectors, leads to aberrant splicing.

Polymerase chain reaction analysis was used to identify aberrant splicing of the simian virus 40 small-t intron present in pRSVcat. We examined factors governing the selection and relative use of aberrant 5' splice sites derived from the chloramphenicol acetyltransferase-coding region. Our results indicated that transcripts from virtually any cDNA positioned upstream of the small-t intron could contain alternative 5' splice sites and therefore be subject to deletions within the protein-coding region.