A method for expressing a heterologous protein in a prokaryotic host cell, comprising the steps of: (a) providing a DNA vector having: (1) a control region operatively linked to a first genetic element encoding a carrier protein capable of expression in the host cell, and (2) a second genetic element encoding the heterologous protein, the second element being embedded within the first element such that the first and second elements are contiguous and in the same reading frame; (b) transforming the host cell with the DNA vector; and (c) expressing a fusion protein of the heterologous protein and the carrier protein, wherein the heterologous protein is joined at its N-terminus to a first domain of the carrier protein and at its C-terminus to a second domain of the carrier protein, and also a method for confirming intact expression of heterologous proteins, as well as fusion proteins, DNA constructs, plasmid vectors and transformed host cells relating to the above methods.