Chromosomal expression vector

A Mini Mu Vector, comprising:

• Mu elements required for replicative transposition which consist essentially of the Mu A and B transposition genes, the two attachment sites attL and attR, and the genes encoding the regulatory proteins cts62 and ner all of which are in the order shown in FIG. 1;
• and
• a Mu mor gene, a mu middle promoter, a ribosome binding site linked to at least one unique restriction site, and a gene encoding a selectable marker all of which are operably linked and in proper reading frame to a DNA insert comprising codons for a heterologous polypeptide.