Construction and in vivo analysis of new split lactose permeases

The capacity of incomplete segments of Escherichia coli lactose permease to form transport-competent complexes in vivo was further tested. Two series of mutant lacY genes were constructed. One encoded N-terminal lactose permease segments of different length. The proteins specified by the other group contained deletions of different length and location within the N-terminal region. Several pairs of such mutant proteins reconstituted active lactose transport. For certain combinations duplications of protein segments were compatible with the formation of an active carrier. Duplication of helices could also be tolerated, when part of a single polypeptide chain.