Lactose Carrier Protein of Escherichia coli Structure and Expression of Plasmids Carrying the Y Gene of the lac Operon

Abstract

The previously described hybrid plasmid pC7 which carries lacI+ O+Δ(Z)Y+ A+ on a 12.3 × 106‐Mr DNA fragment [Teather et al. (1978) Mol. Gen. Genet. 159, 239–248] was partially digested with the restriction endonuclease EcoRI under conditions reducing the recognition sequence to ↓ d(A‐A‐T‐T) and ligated to the vector pBR322. lacY‐carrying inserts of various sizes (Mr, 1.5–4.7 × 106) were obtained. Hybrid plasmid pTE18 (2300‐base‐pair insert) carries part of the I (repressor) gene, the promotor‐operator region, part of the Z (β‐galactosidase) gene, the Y (lactose carrier) gene and part of the A (transacetylase) gene. Upon induction of pTE18‐harbouring strains the Y‐gene product is expressed at a nearly constant rate for several generations and accumulates to a level of 12–16% of the total cytoplasmic membrane protein. Integration into the membrane leads to active carrier as judged by binding and transport measurements. Copyright © 1980, Wiley Blackwell. All rights reserved