CHARACTERIZATION OF THE TOL-PAL REGION OF ESCHERICHIA-COLI K-12 - TRANSLATIONAL CONTROL OF TOLR EXPRESSION BY TOLQ AND IDENTIFICATION OF A NEW OPEN READING FRAME DOWNSTREAM OF PAL ENCODING A PERIPLASMIC PROTEIN

The TolQ, TolR, TolA, TolB, and Pal proteins appear to function in mai ntaining the integrity of the outer membrane, as well as facilitating the uptake of the group A colicins and the DNA of the infecting filame ntous bacteriophages. Sequence data showed that these genes are cluste red in a 6-kb segment of DNA with the gene order orf1 tolQ tolR tolA t olB pal orf2 (a newly identified open reading frame encoding a 29-kD9 protein), Like those containing orf1, bacteria containing an insertion mutation in this gene showed no obvious phenotype. Analysis of beta-g alactosidase activity from fusion constructs in which the lac operon w as fused to various genes in the cluster showed that the genes in this region constitute two separate operons: orf1 tolQRA and tolB pal orf2 . In the orf1 tolQRA operon, translation of tolR was dependent on tran slation of the upstream tolQ region, Consistent with this result, no f unctional ribosome-binding site for TolR synthesis was detected.