malB Region in Escherichia coli K-12: Characterization of New Mutations

Phenotypic characterization and mapping of more than 50 Mal(-) mutations located in the malB region lead one to divide the site for Mal(-)lambdas mutations (formerly called gene malB) in that region, into two adjacent genetic segments malJ and malK. malJ and malK are both involved in maltose permeation. It is suggested that (i) malK and lamB, the only known gene specifically involved in phage lambda adsorption (20), constitute an operon of polarity malK lamB. (ii) malJ and malK correspond to two different genes, and (iii) a promoter for the malK lamB operon is located between malJ and malK. Since lambda receptors and maltose permease are inducible by maltose and absent in malT mutants, it is likely that the expression of the malK lamB operon is controlled by the product of gene malT, the positive regulatory gene of the maltose system.     

Nucleotide sequence of the regulatory region of malB operons in E. coli

The nucleotide sequence of a cloned section of the Escherichia coli chromosome containing the promoter regions of the malB divergent operons was determined. The region of the proximal gene, malE of the malEFG operon, was identified on the basis of the known amino acid sequence of the precursor molecule of maltose-binding protein. The region of malK, the proximal gene of the malKlamB operon, was deduced from the observation that a cloned segment contains an amino-terminal portion of the malK gene. The non-coding region between malE and malK is 299 base pairs long and contains two long GC clusters. Another feature of this region that may be related to the regulation of gene expression is the presence of two palindromic structures between the GC clusters. The DNA regions binding to cyclic AMP binding protein were determined by a method using polyacrylamide gel electrophoresis. The sites are thought to be located close to GC clusters.     

Structure of the malB region in Escherichia coli K12. I. Genetic map of the malK-lamB operon.

Summary A series of deletions, Mu insertions and point mutations affecting the malK-lamB operon have been isolated. They were used to establish a deletion map of this operon, which could be divided in 27 intervals, with 16 in malK and 11 in lamB. One interesting feature of this map is the lack of randomness in the distribution of Mu insertions in the lamB gene; by using data published elsewhere on the physical length of the deletion intervals it can be concluded that about 25% of these Mu insertions are clustered in a segment representing 3% of the gene, and another 20% in a segment representing 2 to 8% of the gene. This map is presently being used to study the biosynthesis, structure, and function of the lamB product, which is an outer membrane protein involved in the transport of maltose and maltodextrin, and which in addition constitutes the receptor for phage .     

Structure of the malB region in Escherichia coli K12. III. Correlation of the genetic map with the restriction map.

A correlation between the genetic and physical maps of the malB region was obtained by performing a restriction cleavage analysis of DNA's carrying various genetically characterized malB deletions. This also allowed to localize the boundaries between malF and malE, malE and malK, mal K and lamB on the restriction map. The genetic map is not grossly distorted with respect to the physical map.     

Interaction of the lamB protein with the peptidoglycan layer in Escherichia coli K12

In Escherichia coli K12 the product of gene lamB is an outer membrane protein involved in the transport of maltose and maltodextrins and serving as a receptor for several bacteriophages including lambda. About 30 to 40% of this protein can be recovered associated to peptidoglycan when the cells are dissolved in sodium dodecyl sulfate in the presence of 2 mM Mg2+ ions. The bound protein can then be quantitatively eluted from peptidoglycan by incubating the complex in Triton X-100 and EDTA, or sodium dodecyl sulfate and NaCl. The protein eluted in such ways is still totally active in its phage-neutralizing activity. Two other membrane proteins known to behave similarly to the lamB protein are proteins Ia and Ib. However the binding of these proteins to peptidoglycan appears tighter, in several respects, than that of the lamB protein. The lamB protein may span the outer membrane since it appears to interact with the peptidoglycan on the inner side of this membrane while it is known to be accessible to both phages and antibodies at the cell surface.     

Dominance study with rifampicin-resistant mutants of E. coli K 12

Summary The location of the characters for rifampicin-resistance in E. coli linked to the arg E marker was confirmed by mating experiments with rifampicin-resistant Hfr C mutants and a rifampicin-sensitive acceptor strain. During these tests, temporary dominance of rifampicin-sensitivity was observed. On the basis of the results obtained, the time required for complete phenotypic expression of rifampicin-resistance was determined, and the ratios of rifampicin-sensitivity to rifampicin-resistance in the merozygote phase of the cell were studied. It was found that the episomal marker of rifampicin-sensitivity influences the level of resistance in merodiploid cells, but does not fully restore the original sensitivity of the wild type.     

The EnvC phenotype and its expression in various Escherichia coli K12 strains

Abstract The septation-deficient mutant of Escherichia coli K12, PM61 envC , has been reported to have many membrane-related anomalies. To distinguish between real pleiotropy and a multimutational phenotype, the envC region was co-transduced with a selectable marker into 4 strains and the phenotypes of the transductants examined. It was found that (1) lysophosphatidylethanolamine accumulation did not cause EnvC morphology, nor was it caused by the envC lesion; (2) a low phosphatidylglycerol/diphosphatidylglycerol ratio (PG/DPG), hypersensitivity to tetracycline and resistance to novobiocin were dissociable from envC by transduction, but hypersensitivity to deoxycholate was not; (3) septation deficiency was expressed to variable degrees in different host strains. Thus, PM61 bears several envelope-related mutations in the 81 min region. The transduction results also suggested that the envC site is slightly upstream from cysE .     

Synthesis of paf-acether by E. coli K12

Paf-acether (platelet-activating factor) is one of the most potent mediator of inflammation released from and acting on most cells that participate in inflammatory diseases. Its molecular structure is 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine. Two metabolic steps are involved in its biosynthesis: the action of a phospholipase A2 on choline-containing membrane alkyl-ether lipids results in the production of lyso paf-acether and acetylation of the lyso compound by an acetyltransferase yields the biologically active molecule. Membrane alkyl-ether lipids can therefore be considered as potential precursors of paf-acether and their composition has been studied in various cell types. In this work, we investigated the presence of paf-acether in E. coli. Our results showed that paf-acether can be obtained from E. coli K12 under a variety of bacterial growth conditions. Paf-acether from E. coli exhibited the same physicochemical and biological characteristics as synthetic paf-acether and that from eucaryotic cells. Therefore, it appears that E. coli itself has the ability of producing paf-acether, a result that could be of some importance with respect to the pathogenesis of Enterobacteria and the use of E. coli in the recombinant DNA technology.