A modified CAT expression vector with convenient cloning sites.

The chloramphenicol acetyl transferase (CAT) gene is widely used as a reporter gene to analyse promoters and other gene regulatory elements. Cloning of a DNA fragment into a CAT vector such as pSVO CAT (1) usually involves blunt-end ligation with no control over the orientation of the insert. This is because the first generation CAT vectors lack convenient multiple restriction sites immediately upstream of the CAT gene. At least two CAT vectors have since been constructed with a multiple cloning site 5' to the CAT gene (2, 3). Both vectors are based on bluescribe Ks . At least one of the vectors (Ks+-SVOCAT) expresses some basal CAT activity in host cells, probably directed by the T7 promoter (2). Also, it has restriction sites within the multiple cloning site that appear elsewhere in the plasmid. As an alternative to the bluescribe series, we have modified the original pSVO vector to incorporate a unique polylinker region which can facilitate both molecular cloning of a DNA fragment as well as controlled deletion of sequence from either end of the insert.