SummaryICEBs1 is a mobile genetic element found in the chromosome of Bacillus subtilis. Excision and transfer of ICEBs1 is regulated by the global DNA damage response and intercellular peptide signalling. We identified and characterized a repressor, ImmR (formerly YdcN), encoded by ICEBs1. ImmR represses transcription of genes required for excision and transfer, and both activates and represses its own transcription. ImmR regulates transcription within ICEBs1 by binding to several sites in the region of DNA that contains promoters for both immR and xis (encoding excisionase). In addition, we found that ImmR confers immunity from acquisition of additional copies of ICEBs1. ImmR-mediated regulation serves to keep a single copy of ICEBs1 stably maintained in the absence of induction, allows a rapid response to inducing signals, and helps limit acquisition of additional copies of ICEBs1.

Southwestern American Indian (Amerindian) mitochondrial DNAs (mtDNAs) were analyzed with restriction endonucleases and found to contain Asian restriction fragment length polymorphisms (RFLPs) but at frequencies very different from those found in Asia. One rare Asian HincII RFLP was found in 40% of the Amerindians. Several mtDNAs were discovered which have not yet been observed on other continents and different tribes were found to have distinctive mtDNAs. Since the mtDNA is inherited exclusively through the maternal lineage, these results suggest that Amerindian tribes were founded by small numbers of female lineages and that new mutations have been fixed in these lineages since their separation from Asia.

A Drosophila laminin A chain gene was characterized as a 14 kb genomic nucleotide sequence which encodes an open reading frame of 3712 amino acids in 15 exons. Overall, this A chain is similar to its vertebrate counterparts, especially in its N‐ and C‐terminal globular domains, but the sequence that forms the laminin A short arm is quite different and larger. Laminin messages appear in newly formed mesoderm and are later prominently expressed in hemocytes, which also synthesize basement membrane collagen IV. The composition of Drosophila basement membranes changes with development. A novel method of tandemly fused RNA probes showed that developmental increases of laminin mRNAs were primarily associated with periods of morphogenesis, and preceded those of collagen IV, a protein strongly expressed during growth. The ratio of A:B1:B2 mRNAs varied little during embryogenesis, with less mRNA for A than B chains. Staining of embryos with antibodies confirmed and extended the information provided by in situ hybridization. Homologs of the G‐subdomains of this A chain, which occur in interacting regions of agrin, perlecan, laminin and sex steroid binding protein, may be involved in protein associations.

Capsular polysaccharide (CPS) is a major virulence factor in Vibrio vulnificus, and encapsulated strains have an opaque, smooth (OpS) colony morphology, while nonencapsulated strains have a translucent, smooth (TrS) colony morphology. Previously, we showed that OpS and TrS parental strains can yield a third colony type, rugose (R), and that the resulting strains, with the OpR and TrR phenotypes, respectively, form copious biofilms. Here we show that while OpR and TrR strains both produce three-dimensional biofilm structures that are indicative of rugose extracellular polysaccharide (rEPS) production, OpR strains also retain expression of CPS and are virulent in an iron-supplemented mouse model, while TrR strains lack CPS and are avirulent. Chlorine resistance assays further distinguished OpR and TrR isolates as exposure to 3 g/ml NaOCl eradicated both OpS and OpR strains, while both TrS and TrR strains survived, but at rates which were significantly different from one another. Taken together, these results further emphasize the importance of CPS for virulence of V. vulnificus and establish a correlation between CPS expression and chlorine sensitivity in this organism. Using reverse transcriptase PCR, we also identified a nine-gene cluster associated with both CPS and rEPS expression in V. vulnificus, designated the wcr (capsular and rugose polysaccharide) locus, with expression occurring primarily in R variants. The latter results set the stage for characterization of functional determinants which individually or collectively contribute to expression of multiple EPS forms in this pathogen.Vibrio vulnificus is a gram-negative marine and estuarine bacterium capable of causing severe disease in susceptible individuals. This bacterium is normally found in fish and shellfish, including oysters. Several medical conditions can predispose a person to being susceptible to infection by this organism, including diabetes, liver disease, hemachromatosis, and a compromised immune system. When people with such conditions consume raw oysters or other seafood containing V. vulnificus, they are at risk of developing a rapidly progressing primary septicemia that can be fatal within 24 to 48 h. In an otherwise healthy individual, if a break in the skin is exposed to seawater containing this organism, a severe wound infection may develop that could necessitate amputation if treatment is not begun soon after the onset of symptoms. V. vulnificus does not infect as many people as other members of the genus Vibrio, but it is the leading reported cause of death from the consumption of seafood in the United States (28, 48).V. vulnificus produces several virulence factors, including multiple enzymes, siderophores, RtxA toxin, and a polysaccharide capsule (for a review, see reference 15). While the other factors may assist in virulence, the capsular polysaccharide (CPS) is considered a major virulence factor and has been reported to protect the bacteria from phagocytosis and complement-mediated killing by the host immune system. When grown ...

Laminins are trimeric glycoproteins composed of A, B1, and B2 chains that play important roles in cell adhesion and differentiation and in the assembly of basement membranes. There is evidence that multiple independent gene products can be used to supply the A, B1, and B2-like chains, thereby generating diverse laminin molecules. The set of A chain-like polypeptides are the most divergent. The amino-terminal portion of each chain, called the short arm, is composed of alternating cysteine-rich and globular domains. The amino-terminal two-thirds of the newly characterized Drosophila laminin A chain appears to encode a novel structure, but the analysis presented here shows that substantial portions of its amino acid sequence are related to sequences found in other A, B1, and B2 chains. A portion of the Drosophila A chain is composed of sequences like those found in B2 chains. These sequences parallel a portion of the vertebrate A chains, suggesting a structure for a shared ancestral A chain. However, unlike vertebrate A chains, the Drosophila A chain also contains sequences typical of B1 chains, suggesting that its gene must have arisen by recombination of segments from different primordial laminin genes.