Expression and stability of the hepatitis B pol protein in Escherichia coli

The pGEX plasmid containing the gene of glutathione S‐transferase (GST) was employed to express various lengths of the hepatitis B virus pol protein in a form of fusion protein in Escherichia coli. Results of SDS‐PAGE and Western blot analyses indicated that: (i) expression of GST‐pol fusion proteins varied from undetectable to 30% of total protein in different clones; (ii) presence of the carboxyl terminus of the pol protein apparently lowered the expression amount of fusion proteins; (iii) some distinct pol protein bands of lower molecular weight were constantly detected in several clones. The presence of the smaller pol protein therefore raises a possibility that the pol protein contains protease cutting sites.