Sequence of the mglB gene from Escherichia coli K12: comparison of wild-type and mutant galactose chemoreceptors

Summary The mglB gene of Escherichia coli codes for a galactose-binding protein (GBP) that serves both as the galactose chemoreceptor and as the recognition component of the -methylgalactoside transport system. The mglB551 mutation eliminates the chemotactic function of GBP without altering its transport or substrate-binding properties. To investigate the interaction between GBP and Trg, the chemotactic signal transducer for galactose, we sequenced the mglB genes from wild-type and mglB551 mutant strains. The mutation causes the replacement of Gly₇₄ of GBP by Asp. This residue is located in alpha-Helix III at the tip of the P domain in the GBP tertiary structure farthest removed from the substrate-binding cleft between the P and Q domains. We conclude that Helix III must be part of, or at least adjacent to, the recognition site for Trg. Our sequence also included part of the mglA gene, which is immediately distal to mglB. The amino acid sequence deduced for the beginning of the MglA protein showed homology with a family of polypeptides that contain an ATP-binding site and are components of binding-protein-dependent transport systems.     

Comparison of sequences from the malB regions of Salmonella typhimurium and Enterobacter aerogenes with Escherichia coli K12: A potential new regulatory site in the interoperonic region

Summary The malE and malK genes from Salmonella typhimurium, and the MalEFG operon and a portion of malK from Enterobacter aerogenes were cloned and sequenced. Plasmid-borne malE genes from both species and the malF and malG genes from E. aerogenes were expressed normally in Escherichia coli, and their products function in maltose transport. This shows that the malB products from the three species are interchangeable, at least in the combinations tested. The general genetic organization of the malB region is conserved. Potential binding sites and distances between them are highly conserved in the regulatory intervals. An unexpected conserved region was detected, which we call the U box, and which could be another target for a regulatory protein. This hypothesis is supported by the presence of the U box in the regulatory, region of the pulA-malX operon in Klebsiella pneumoniae. The intergenic region between malE and malF from S. typhimurium and E. aerogenes, contains inverted repeats similar to the palindromic units (PU or REP) found at the same location in E. coli. The predicted amino acid sequence of the encoded proteins showed 90% or more identity in every pairwise comparison of species.     

The effect of rigid fixation on growth of the neurocranium

The effects on skull growth of plating the coronal suture and frontal bone were studied in New Zealand White rabbits. Three-dimensional coordinate landmarks were digitized and analyzed to determine the differences in form between operated and unoperated animals using Euclidian distance matrix analysis. This method compares sets of interlandmark distances in three dimensions and was used to demonstrate changes induced by plating. We interpret these changes in morphology to be the result of differences in growth between the operated and unoperated groups. Periosteal elevation alone (n = 6) resulted in a minimal local growth increase. Coronal suture plating (n = 8) resulted in local growth restriction with contralateral and adjacent size increases. Frontal bone plating (n = 6) without crossing a suture line also resulted in local growth restriction and adjacent bone size increases. The timing of intervention in relation to the completion of bone growth may explain the magnitude of clinically apparent effects. Changes in bones adjacent to those directly manipulated may be an attempt to maintain a normal skull volume.     

Evolution of chemotactic-signal transducers in enteric bacteria.

The methyl-accepting chemotactic-signal transducers of the enteric bacteria are transmembrane proteins that consist of a periplasmic receptor domain and a cytoplasmic signaling domain. To study their evolution, transducer genes from Enterobacter aerogenes and Klebsiella pneumoniae were compared with transducer genes from Escherichia coli and Salmonella typhimurium. There are at least two functional transducer genes in the nonmotile species K. pneumoniae, one of which complements the defect in serine taxis of an E. coli tsr mutant. The tse (taxis to serine) gene of E. aerogenes also complements an E. coli tsr mutant; the tas (taxis to aspartate) gene of E. aerogenes complements the defect in aspartate taxis, but not the defect in maltose taxis, of an E. coli tar mutant. The sequence was determined for 5 kilobases of E. aerogenes DNA containing a 3' fragment of the cheA gene, cheW, tse, tas, and a 5' fragment of the cheR gene. The tse and tas genes are in one operon, unlike tsr and tar. The cytoplasmic domains of Tse and Tas are very similar to those of E. coli and S. typhimurium transducers. The periplasmic domain of Tse is homologous to that of Tsr, but Tas and Tar are much less similar in this region. However, several short sequences are conserved in the periplasmic domains of Tsr, Tar, Tse, and Tas but not of Tap and Trg, transducers that do not bind amino acids. These conserved regions include residues implicated in amino-acid binding.     

Le Fort fractures without mobility

The Le Fort fracture without maxillary mobility constitutes 9 percent of maxillary fractures observed over a 3-year period. A high Le Fort (level II or III) injury exists as a one- or two-piece incomplete fracture. The degree of fracture is insufficient to permit mobility of the maxillary alveolus. Frequently, an obvious unilateral zygomatic fracture is present. Physical findings consist of bilateral eyelid ecchymosis and malocclusion. The occlusal disturbance may consist of either crossbite, open bite, maxillary rotation, or lack of proper dental intercuspation. On CT scan, fractures are best demonstrated in the posterior and medial maxillary walls at the Le Fort I level; they are most obvious unilaterally with contralateral fractures that may be subtle. Bilateral maxillary sinus fluid is consistently present on CT. Treatment usually consists of observation and traction elastics but may require mobilization of the fragments followed by open reduction and rigid fixation.     

Vaccine protection by a triple deletion mutant of simian immunodeficiency virus.

Twelve rhesus monkeys were vaccinated with SIVmac316 delta nef (lacking nef sequences), and 12 were vaccinated with SIVmac239 delta3 (lacking nef, vpr, and upstream sequences in U3). SIVmac316 and SIVmac239 differ by only eight amino acids in the envelope; these changes render SIVmac316 highly competent for replication in macrophages. Seventeen of the animals developed persistent infections with the vaccine viruses. Seven of the 24 vaccinated animals, however, developed infections that were apparently transient in nature. Six of these seven yielded virus from peripheral blood when tested at weeks 2 and/or 3, three of the seven had transient antibody responses, but none of the seven had persisting antibody responses. The 24 monkeys were challenged in groups of four with 10 rhesus monkey infectious doses of wild-type, pathogenic SIVmac251 at weeks 8, 20, and 79 following receipt of vaccine. None of the seven with apparently transient infections with vaccine virus were protected upon subsequent challenge. Analysis of cell-associated viral loads, CD4+ cell counts, and viral gene sequences present in peripheral blood in the remainder of the monkeys following challenge allowed a number of conclusions. (i) There was a trend toward increased protection with length of time of vaccination. (ii) Solid vaccine protection was achieved by 79 weeks with the highly attenuated SIV239 delta3. (iii) Solid long-term protection was achieved in at least two animals in the absence of complete sterilizing immunity. (iv) Genetic backbone appeared to influence protective capacity; animals vaccinated with SIV239 delta3 were better protected than animals receiving SIV316 delta nef. This better protection correlated with increased levels of the replicating vaccine strain. (v) The titer of virus-neutralizing activity in serum on the day of challenge correlated with protection when measured against a primary stock of SIVmac251 but not when measured against a laboratory-passaged stock. The level of binding antibodies to whole virus by enzyme-linked immunosorbent assay also correlated with protection.     

Sons of low-ranking female rhesus macaques can attain high dominance rank in their natal groups

Five adult and subadult sons of middle- and low-ranking female rhesus macaques (Macaca mulatta) were observed to hold high dominance rank in their natal groups during a 12-month study at Cayo Santiago, Puerto Rico. Three of these males also experienced high mating success during at least one mating season. These findings contrast with all previously published accounts of rank acquisition by natal male rhesus macaques in provisioned colonies, and they present a challenge to the hypothesis that natal transfer functions to increase male access to fertile females.     

Maltose chemotaxis involves residues in the N-terminal and C-terminal domains on the same face of maltose-binding protein.

The periplasmic maltose-binding protein (MBP) of Escherichia coli is the recognition component of the maltose chemoreceptor and of the active transport system for maltose. It interacts with the Tar chemotactic signal transducer and the integral cytoplasmic-membrane components (the MalF and MalG proteins) of the maltose transport system. Maltose binds in a cleft between the globular N-terminal and C-terminal domains of MBP, which are connected by a moveable hinge. The two domains undergo a large motion relative to one another as the protein moves from the open, unbound state to the closed, ligand-bound state. We generated, by doped-primer mutagenesis, amino acid substitutions that specifically disrupt the chemotactic function of MBP. These substitutions cluster in two well-defined regions that are nearly contiguous on the surface of MBP in its closed conformation. One region is in the N-terminal domain and one is in the C-terminal domain. The distance between the two regions is expected to change substantially as the protein goes from the open to the closed form. These results support a model in which ligand binding brings two recognition sites on MBP into the proper spatial relationship to interact with complementary sites on Tar. Mutations in MBP that appear to cause defects in interaction with MalF and MalG are distributed differently from mutations that primarily affect maltose taxis. We conclude that the regions of MBP that contact Tar and those that contact MalF and MalG are adjacent on the face of the protein opposite the hinge connecting the two domains and that those regions are largely, although perhaps not entirely, distinct.