Mammalian gene expression is improved by use of a longer SV40 early polyadenylation cassette.

Expression vectors normally contain sequences that stimulate polyadenylation of the expressed mRNA. These sequences usually include an AATAAA consensus sequence 20-30 nucleotides 5' of a diffuse GTor T-rich stretch immediately following the sequences that form the 3' end of the mRNA. The efficiency of the two minimal elements is also influenced by additional upor downstream elements (1). Very often polyadenylation sequences are taken from the viral SV40 genome. The minimal functional cassette is a 237 bp Bell (2770)-BamHI (2533) restriction fragment of the SV40 genome containing the cleavage/polyadenylation signals of the early and the late transcription units, depending on the orientation (2). In commercially available vectors the fragment is frequently used in the early orientation. However, sometimes a longer cassette of the early polyadenylation sequences is used. This cassette contains a 988 bp restriction fragment from Bell (2770) up to EcoRI (1782), i.e. extending into the 3' end of the VP1 coding region (3).