CLONING AND ORGANIZATION OF THE ABC AND MDL GENES OF ESCHERICHIA-COLI- RELATIONSHIP TO EUKARYOTIC MULTIDRUG-RESISTANCE

Using degenerate oligodeoxyribonucleotides from conserved regions of t he gene family encoding ATP-binding domain of the active transporter, two new Escherichia coli genes were identified. The first of the genes , named mdl (multidrug resistance-like), is located at min 10.2 of the E. coli chromosome and encodes two ATP-binding motifs and two hydro-p hobic (transmembrane) domains. The ATP-binding domains of mdl show 35- 38% amino acid (aa) identity with members of the eukaryotic P-glycopro tein/multidrug resistance family. To date, 25 members of the ATP-trans porter/permease gene family have been characterized in E. coli. Compar ison of the ATP-binding domains from this family indicates that mdl is part of a distinct subfamily of sequences that includes hlyB, msbA, a nd cvaB. Gene-disruption studies revealed that mdl is not essential fo r cell growth. The second open reading frame, named nbc (ATP-binding c assette), is located at min 4.9 of the chromosome, encodes a single AT P-binding domain, and is most homologous to ftsE, a cell division cont rol gene of E. coli. The abe gene product also shows aa sequence homol ogy to several E. coli permeases.