A mutant poliovirus containing a novel proteolytic cleavage site in VP3 is altered in viral maturation.

A six-amino-acid insertion containing a Q-G amino acid pair was introduced into the carboxy terminus of the capsid protein VP3 (between residues 236 and 237). Transfection of monkey cells with full-length poliovirus cDNA containing the insertion described above yields a mutant virus (Sel-1C-02) in which cleavage occurs almost entirely at the inserted Q-G amino acid pair instead of at the wild-type VP3-VP1 cleavage site. Mutant Sel-1C-02 is delayed in the kinetics of virus production at 39 degrees C and exhibits a defect in VP0 cleavage into VP2 and VP4 at 39 degrees C. Sucrose gradient analysis of HeLa cell extracts prepared from cells infected by Sel-1C-02 at 39 degrees C shows an accumulation of fast-sedimenting replication-packaging complexes and a significant amount of uncleaved VP0 present in fractions containing mature virions. Our data provide in vivo evidence for the importance of determinants other than the conserved amino acid pair (Q-G) for recognition and cleavage of the P1 precursor by proteinase 3CD and show that an alteration in the carboxy terminus of VP3 or the amino terminus of VP1 affects the process of viral maturation.     

Both CheA and CheW are required for reconstitution of chemotactic signaling in Escherichia coli.

If cells of Escherichia coli deleted for genes that specify transducers and all known cytoplasmic chemotaxis proteins are reconstituted with CheA, CheW, and CheY, they spin their flagella alternately clockwise and counterclockwise. If the aspartate receptor also is present, clockwise rotation is suppressed upon addition of aspartate. If either CheA or CheW is absent, the fraction of time that the flagella spin clockwise is reduced and responses to aspartate do not occur.     

Activation of the c-H-ras proto-oncogene by retrovirus insertion and chromosomal rearrangement in a Moloney leukemia virus-induced T-cell leukemia.

A rearrangement of the c-H-ras locus was detected in a T-cell line (DA-2) established from a Moloney leukemia virus-induced tumor. This rearrangement was associated with the high-level expression of H-ras RNA and the H-ras gene product, p21. DNA from DA-2 cells transformed fibroblasts in DNA transfection experiments, and the transformed fibroblasts contained the rearranged H-ras locus. The rearrangement involved one allele and was present in tissue from the primary tumor from which the cell line was isolated. Cloning and sequencing of the rearranged allele and comparison with the normal allele demonstrated that the rearrangement was complex and probably resulted from the integration of a retrovirus in the H-ras locus between a 5' noncoding exon and the first coding exon and a subsequent homologous recombination between this provirus and another newly acquired provirus also located on chromosome 7. These events resulted in the translocation of the coding exons of the H-ras locus away from the 5' noncoding exon region to a new genomic site on chromosome 7. Sequencing of the coding regions of the gene failed to detect mutations in the 12th, 13th, 59th, or 61st codons. The possible reasons for the complexity of the rearrangement and the significance of the activation of the H-ras locus to T-cell transformation are discussed.     

Torque generation in the flagellar motor of Escherichia coli: evidence of a direct role for FliG but not for FliM or FliN.

Among the many proteins needed for assembly and function of bacterial flagella, FliG, FliM, and FliN have attracted special attention because mutant phenotypes suggest that they are needed not only for flagellar assembly but also for torque generation and for controlling the direction of motor rotation. A role for these proteins in torque generation is suggested by the existence of mutations in each of them that produce the Mot- (or paralyzed) phenotype, in which flagella are assembled and appear normal but do not rotate. The presumption is that Mot- defects cause paralysis by specifically disrupting functions essential for torque generation, while preserving the features of a protein needed for flagellar assembly. Here, we present evidence that the reported mot mutations in fliM and fliN do not disrupt torque-generating functions specifically but, instead, affect the incorporation of proteins into the flagellum. The fliM and fliN mutants are immotile at normal expression levels but become motile when the mutant proteins and/or other, evidently interacting flagellar proteins are overexpressed. In contrast, many of the reported fliG mot mutations abolish motility at all expression levels, while permitting flagellar assembly, and thus appear to disrupt torque generation specifically. These mutations are clustered in a segment of about 100 residues at the carboxyl terminus of FliG. A slightly larger carboxyl-terminal segment of 126 residues accumulates in the cells when expressed alone and thus probably constitutes a stable, independently folded domain. We suggest that the carboxyl-terminal domain of FliG functions specifically in torque generation, forming the rotor portion of the site of energy transduction in the flagellar motor.     

A cellular cofactor facilitates efficient 3CD cleavage of the poliovirus P1 precursor.

The production of poliovirus capsid proteins from a capsid protein precursor (P1) is mediated by virus-encoded proteinase 3CD and involves a complicated set of proteinase-substrate interactions. In addition to substrate and enzymatic determinants required for this interaction, we describe a cellular cofactor, which facilitates 3CD recognition of the P1 precursor. Cellular cofactor activity is 3CD dependent and salt dependent. Our analysis shows that proteolytic cleavage of the P1 precursor at the VP0/VP3 cleavage site exhibits a greater dependency on the cellular cofactor than cleavage at the VP3/VP1 site. Such a greater dependency on cellular cofactor activity can be relieved (in part) by the substitution of an Ala residue for the Pro residue at the -4 position of the VP0/VP3 cleavage site. However, mutant viruses containing Pro-to-Ala substitutions at the -4 position of the VP0/VP3 site exhibit defects in viral growth.     

A phenotypic host range alteration determines RD114 virus restriction in feline embryonic cells.

We have characterized the restriction mechanism for RD114 virus replication in embryonic feline cells (FeF). By comparing growth properties of the virus in FeF cells with its behavior in a fetal feline glial cell line (G355) permissive for RD114, we showed that both cell lines were readily infectible by virus grown in permissive cells and that no significant differences in viral integration or viral RNA expression could be detected. However, analysis of viral protein expression revealed differences in viral env gene processing in the two cell types. Envelope precursor pR85 was produced, but the expected processed gp70 product was detectable only in permissive (G355) cells. An envelope product of 85 kDa was packaged into virions produced by FeF cells, while virions produced by G355 cells contained the expected RD114 gp70. While the gp85 env-containing virions were infectious for permissive G355 cells, they were unable to infect FeF cells. The block to infection by the gp85-containing particles in FeF cells could be abrogated by treatment with the glycosylation inhibitor tunicamycin. Our results indicate that restriction of RD114 virus involves a novel mechanism dependent on two factors: altered glycosylation of the envelope to a gp85 form and an altered RD114 receptor in FeF cells.     

Randomised controlled trial of oxytocin alone versus oxytocin and ergometrine in active management of third stage of labour.

OBJECTIVE--To compare intramuscular oxytocin alone and intramuscular oxytocin with ergometrine (Syntometrine) for their effect in reducing the risk of postpartum haemorrhage when both are used as part of the active management of the third stage of labour. DESIGN--Double blind, randomised controlled trial. SETTING--Two metropolitan teaching hospitals in Perth, Western Australia. SUBJECTS--All women who expected a vaginal birth during the period of the trial. Informed consent was obtained. MAIN OUTCOME MEASURES--Postpartum haemorrhage, nausea, vomiting, and increased blood pressure. RESULTS--3497 women were randomly allocated to receive oxytocin-ergometrine (n = 1730) or oxytocin (n = 1753). Rates of postpartum haemorrhage (> or = 500 ml or > or = 1000 ml) were similar in both arms (odds ratio 0.90 (0.82); 95% confidence interval 0.75 to 1.07 (0.59 to 1.14) at 500 ml (1000 ml) threshold). The use of oxytocin-ergometrine was associated with nausea, vomiting, and increased blood pressure. CONCLUSIONS--There are few advantages but several disadvantages for the routine use of oxytoxinergometrine when prophylactic active management of the third stage of labour is practised. Further investigation of dose-response for oxytocin may be warranted.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.