To directly express native recombinant proteins in Escherichia coli, a new expression vector pSB was constructed using Ssp DnaB mini-intem. Using the vector, native proteins could be produced with the help of C-terminal self-cleavage of the intein. In this study, we cloned hIFN alpha-4 gene into pSB and used E coli strain Origami B (DE3) as the host. Expression experiments were carried out both in Shake flasks and a 5 L bioreactor. The results indicated hIFN alpha-4 could be expressed in the form of soluble protein with correct folding in E coli. The maximal hIFN alpha-4 content was 21.7% of total protein, and the antiviral activity of the protein was 1.2 x 10(8) IU mg(-1). Overall, good effects were achieved with this system. This intein-mediated protein expression system opens up a useful method for production of native recombinant protein in E coli. (c) 2005 Elsevier Inc. All rights reserved.