chapter  2
60 Pages

The Biosynthesis of Bacterial Outer Membrane Proteins

The ompA gene, which maps at 21 min on the E. coli chromosome, ' 7·30·75 is the structural gene for OmpA protein. This protein has a mol wt of 35,20076 and is the only protein among the major outer-membrane proteins which can be partially digested with trypsin or pronase when the whole cell envelope or outer membrane is enzymatically treated. 77 -79 This indicates that part of OmpA protein is exposed on the outer surface of the membrane. OmpA protein exhibits anomalous heat modifiability on SDS-polyacrylamide gels with its apparent molecular weight increasing when the membrane is solubilized in SDS above 50°C. 22 ·77 ·80·81 Purified OmpA protein inhibits conjugation, 82·83 inactivates the phages K3 83 and Tull*, 84 and ompA mutants are found among those cells which are tolerant to colicin L, 85 resistant to phages K3 86 or Tull*, 34

chromosome. Therefore, the S. typhimurium ompA gene is situated in the same position as the E. coli ompA gene. 72

TheJamBgeneisthestructuralgeneforAreceptorproteinandislocatedwithinthe malBregionat90minontheE.colichromosomalmap. 17 "111TheA.receptorproteinis involvedinthetransportofmaltoseandmaltodextrans.' 12·113AsdescribedinSection

III.D.l,JamBispositivelyregulatedbytheproductofthemalTgenewhichmapsat

75min.114FusionsofthelamBgenetothelacZgenehavebeenconstructed,andprovideameansforstudyingouter-membraneproteinlocalization115(seeSectionIV).