Mechanisms of increasing expression of a yeast gene in Escherichia coli.

Escherichia coli strains w?th increased expression of t’he cloned yeast his3 gene were selected. In some mutants an E. co/i chromosomal locus is altered; in others the yrast his3 sequence is affected. Alterations of the his3 sequence include a point mutation, deletion, and IS2 insert’ion. When IS2 insert’s into the yeast sequence, all pre-existing copies of IS2 are maintained in t,heir original 1ocat)ion in tile E. coli chromosome. The results indicate that E. coli can employ a variety of meclkanisms to increase expression of a foreign gone.