The complete mitochondrial genome (mitogenome) of the fall webworm, Hyphantria cunea (Lepidoptera: Arctiidae) was determined. The genome is a circular molecule 15 481 bp long. It presents a typical gene organization and order for completely sequenced lepidopteran mitogenomes, but differs from the insect ancestral type for the placement of tRNAMet. The nucleotide composition of the genome is also highly A + T biased, accounting for 80.38%, with a slightly positive AT skewness (0.010), indicating the occurrence of more As than Ts, as found in the Noctuoidea species. All protein-coding genes (PCGs) are initiated by ATN codons, except for COI, which is tentatively designated by the CGA codon as observed in other lepidopterans. Four of 13 PCGs harbor the incomplete termination codon, T or TA. All tRNAs have a typical clover-leaf structure of mitochondrial tRNAs, except for tRNASer(AGN), the DHU arm of which could not form a stable stem-loop structure. The intergenic spacer sequence between tRNASer(AGN) and ND1 also contains the ATACTAA motif, which is conserved across the Lepidoptera order. The H. cunea A+T-rich region of 357 bp is comprised of non-repetitive sequences, but harbors several features common to the Lepidoptera insects, including the motif ATAGA followed by an 18 bp poly-T stretch, a microsatellite-like (AT)8 element preceded by the ATTTA motif, an 11 bp poly-A present immediately upstream tRNAMet. The phylogenetic analyses support the view that the H. cunea is closerly related to the Lymantria dispar than Ochrogaster lunifer, and support the hypothesis that Noctuoidea (H. cunea, L. dispar, and O. lunifer) and Geometroidea (Phthonandria atrilineata) are monophyletic. However, in the phylogenetic trees based on mitogenome sequences among the lepidopteran superfamilies, Papillonoidea (Artogeia melete, Acraea issoria, and Coreana raphaelis) joined basally within the monophyly of Lepidoptera, which is different to the traditional classification.

Background-Shigella enterotoxin 1 is a novel enterotoxin elaborated by Shigella flexneri 2a that causes fluid accumulation in rabbit ileal loops and a rise in short circuit current in Ussing chambers. Aims-To gain insights into the mechanism of action of shigella enterotoxin 1. Methods-Supernatants from genetically engineered clones either overexpressing shigella enterotoxin 1 or producing deletion mutants of the toxin were tested in rabbit ileum both in vitro and in vivo. Results-In rabbit ileum shigella enterotoxin 1 induced an irreversible rise in short circuit current that was not mediated by any of the recognised intracellular mediators of secretion. Deletion of 90% of the A subunit of the holotoxin ablated its enterotoxicity. In the in vivo perfusion model, the toxin induced a time dependent decrease in water absorption, whereas no changes were detected in the segment perfused with supernatants obtained from the deletion mutant. Finally, partially purified toxin induced a dose dependent increment in short circuit current that reached its plateau at a toxin concentration of 4x 10 ' M.Conclusions-Shigella enterotoxin 1 induces a time and dose dependent intestinal secretion in the rabbit mal model, suggesting that it may be responsible for the watery phase of Shigella flexneri 2a infection. (Gut 1997; 40: 505-511)

The human monocytic cell line U937 pos- The rapid hydrolysis of phosphatidylinositol 4,5-bisphosphate (Ptdlns-4,5-P2) by phospholipase C (PLC) to two second messengers, inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) and diacylglycerol, is an early event common to many cell types activated by transmembrane signals. Ins-1,4,5-P3 elicits the release of Ca2+ from intracellular stores by binding to a specific receptor (4), and diacylglycerol activates protein kinase C. There are at least seven PLC isozymes in mammalian tissues (5), and different isozymes appear to be activated by different mechanisms. Thus, PLC-yl is activated through phosphorylation at multiple tyrosine residues (6-9), whereas PLC-/31 is selectively activated by a guanine nucleotide binding protein (10, 11). The receptors for epidermal growth factor and plateletderived growth factor are protein tyrosine kinases that directly phosphorylate PLC-y1 on three or four tyrosine residues (9, 12). The tyrosine-phosphorylation-dependent activation of PLC-yl is also observed in response to ligation of the T-cell receptor (TCR) complex on T cells (13,14), the membrane IgM (mIgM) on B cells (15), and the high-affinity Fc receptor for IgE (FceRI) on RBL2H3 cells (16). These results suggest that activation of PLC-yl by tyrosine phosphorylation is not restricted to receptor tyrosine kinases but may also be achieved through nonreceptor tyrosine kinases whose functions are coupled to plasma membrane receptors.Cross-linking of FcyRIII on NK cells by ligand results in an increase in the free intracellular Ca2+ concentration ([Ca2+],) that is mediated by Ins-1,4,5-P3 generated from receptor-dependent hydrolysis of Ptdlns-4,5-P2 (17). Aggregation of FcyRIII on NK cells also results in activation of a nonreceptor tyrosine kinase (18). Therefore, the Fc'yRIIImediated hydrolysis of PtdIns-4,5-P2 in NK cells may also be mediated by phosphorylation of PLC-yl on tyrosine residues. $To whom reprint requests should be addressed. 3659The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Based upon the lipopolysaccharide (LPS) structure and antigenicity of Shigella group B, a strategy for broad cross-protection against 14 Shigella flexneri serotypes was designed. This strategy involves the use of two S. flexneri serotypes (2a and 3a), which together bear the all of the major antigenic group factors of this group. The novel attenuated strains used in these studies were S. flexneri 2a strain CVD 1207 (ΔguaB-A ΔvirG Δset1 Δsen) and S. flexneri 3a strain CVD 1211 (ΔguaB-A ΔvirG Δsen). Guinea pigs were immunized with an equal mixture of these strains and later challenged (Sereny test) with a wild-typeS. flexneri serotype 1a, 1b, 2b, 4b, 5b, Y, or 6 strain of demonstrated virulence in the same model. Guinea pigs that were immunized with these two vaccine strains produced serum and mucosal antibodies that cross-reacted with all the S. flexneri serotypes tested (except of S. flexneriserotype 6) as assessed by enzyme-linked immunosorbent assay, immunoblotting, and slide agglutination. Furthermore, the combination vaccine conferred significant protection against challenge withS. flexneri serotypes 1b, 2b, 5b, and Y but not with serotypes 1a, 4b, or (as predicted) 6.