The pGEMEX?Vectors(a,b) are T7 expression vectors that can be used for cloning, as templates for in vitro transcription and for production of single-stranded DNA (ssDNA). Expression from the pGEMEX?Vectors is based on the T7 expression system (a) developed by Studier (1), which uses a convenient vector/host combination for high-level expression of cloned genes in vivo. Sequences cloned into the pGEMEX? Vectors are expressed as T7 gene 10 fusion proteins in JM109(DE3)(a) or BL21(DE3)pLysS(c) host strains containing an inducible gene for T7 RNA polymerase. JM109(DE3) is a specially constructed host strain that contains an IPTGinducible gene for T7 RNA polymerase; JM109(DE3) and JM109 are supplied with the pGEMEX?Vectors. The pGEMEX?-1 and pGEMEX?-2 Vectors differ by only two base pairs resulting in a shift in the reading frame (Figure 1). The bacteriophage T7 gene 10 leader peptide (260 amino acids) is expressed very efficiently in this host and can accumulate to greater than 50% of total cell protein in three hours or less. Typical levels of fusion protein production are on the order of 10mg per liter of induced culture.