Characterization of Bacillus pumilus E601 Spores After Single Sublethal Gamma Irradiation Treatments

Eighteen survivor strains of Bacillus pumilus E601 have been isolated after single sublethal irradiation treatments with ⁶⁰Co. Primary isolation was based on the loss of motility and pellicle formation. However, with subsequent subcultivation, eight isolates reverted back to the standard of exhibiting motility and pellicle formation. Characteristics of the isolates include alterations in spore radiation resistance and in the amino acid requirements for spore germination and outgrowth. Other alterations in cultural and physiological characteristics were found. Three of the isolates were asporogenous.     

T cell recognition of a tumor-associated glycoprotein and its synthetic carbohydrate epitopes: stimulation of anticancer T cell immunity in vivo

Summary The Thomsen, Friedenreich (TF) and Tn carbohydrate antigens are expressed on the vast majority of human adenocarcinomas and are associated with aggressive behavior of certain tumors. TF and Tn antigens are also expressed on certain murine cancer cell lines including TA3-Ha, a highly lethal, transplantable mammary adenocarcinoma. TF and Tn cancer-associated carbohydrate haptens were synthesized, conjugated to protein carriers and used to demonstrate that delayed-type hypersensitivity (DTH) effector T cells can specifically recognize and respond to carbohydrate determinants on the TA3-Ha tumor-associated glycoprotein, epiglycanin. The effector cells were shown to have the helper DTH phenotype (Lytl⁺, Lyt2^–, Thyl⁺) and it was demonstrated that they respond to specific carbohydrate determinants in an MHC-restricted fashion. These experiments provide the rationale for the use of synthetic tumor-associated glycoconjugates (S-TAGs) to stimulate anticancer T cell immunity. In support of this hypothesis, it was shown that preimmunization with the appropriate S-TAGs could provide a degree of protection against a subsequent tumor transplant and that antitumor effector Lytl⁺, Lyt2^– T cells could be generated in vitro using the appropriate S-TAGs as antigens.     

Structural correlates of recurrent collateral interneurons producing both electrical and chemical inhibitions of the Mauthner cell.

Intracellular injections of horseradish peroxidase provided a basis for morphological identification of inhibitory interneurons belonging to the recurrent collateral network of the Mauthner cell. Their axons dilate to form unusually large bulbs surrounding the axon cap. The morphological appearance of these bulbs as well as intracellular recordings at their level indicate that they behave as nodes and serve as a final source of current for electrical inhibition of the Mauthner cell. The axon of each interneuron gives rise to two different groups of fibres which are respectively fitted for the mediation of electrical and chemical inhibitions of their target cell.     

Role of methylotrophy during symbiosis between Methylobacterium nodulans and Crotalaria podocarpa

Some rare leguminous plants of the genus Crotalaria are specifically nodulated by the methylotrophic bacterium Methylobacterium nodulans. In this study, the expression and role of bacterial methylotrophy were investigated during symbiosis between M. nodulans, strain ORS 2060T, and its host legume, Crotalaria podocarpa. Using lacZ fusion to the mxaF gene, we showed that the methylotroph genes are expressed in the root nodules, suggesting methylotrophic activity during symbiosis. In addition, loss of the bacterial methylotrophic function significantly affected plant development. Indeed, inoculation of M. nodulans nonmethylotroph mutants in C. podocarpa decreased the total root nodule number per plant up to 60%, decreased the whole-plant nitrogen fixation capacity up to 42%, and reduced the total dry plant biomass up to 46% compared with the wild-type strain. In contrast, inoculation of the legume C. podocarpa with nonmethylotrophic mutants complemented with functional mxa genes restored the symbiotic wild phenotype. These results demonstrate the key role of methylotrophy during symbiosis between M. nodulans and C. podocarpa.     

Analysis of Msx1; Msx2 double mutants reveals multiple roles for Msx genes in limb development

The homeobox-containing genes Msx1 and Msx2 are highly expressed in the limb field from the earliest stages of limb formation and, subsequently, in both the apical ectodermal ridge and underlying mesenchyme. However, mice homozygous for a null mutation in either Msx1 or Msx2 do not display abnormalities in limb development. By contrast, Msx1; Msx2 double mutants exhibit a severe limb phenotype. Our analysis indicates that these genes play a role in crucial processes during limb morphogenesis along all three axes. Double mutant limbs are shorter and lack anterior skeletal elements (radius/tibia, thumb/hallux). Gene expression analysis confirms that there is no formation of regions with anterior identity. This correlates with the absence of dorsoventral boundary specification in the anterior ectoderm, which precludes apical ectodermal ridge formation anteriorly. As a result, anterior mesenchyme is not maintained, leading to oligodactyly. Paradoxically, polydactyly is also frequent and appears to be associated with extended Fgf activity in the apical ectodermal ridge, which is maintained up to 14.5 dpc. This results in a major outgrowth of the mesenchyme anteriorly, which nevertheless maintains a posterior identity, and leads to formation of extra digits. These defects are interpreted in the context of an impairment of Bmp signalling.     

How essential are nonessential genes?

Gene essentiality in bacteria has been identified in silico, focusing on gene persistence, or experimentally, focusing on the growth of knockouts in rich media. Comparing 55 genomes of Firmicutes and Gamma-proteobacteria to identify the genes which, while persistent among genomes, do not lead to a lethal phenotype when inactivated, we show that the characteristics of persistence, conservation, expression, and location are shared between persistent nonessential (PNE) genes and experimentally essential genes. PNE genes show an overrepresentation of genes related to maintenance and stress response. This outlines the limits of current experimental techniques to define gene essentiality and highlights the essential role of genes implicated in maintenance which, although dispensable for growth, are not dispensable from an evolutionary point of view. Firmicutes and Gamma-proteobacteria are mostly differing in the construction of the cell envelope, DNA replication and proofreading, and RNA degradation. In addition to suggesting functions for persistent genes that had until now resisted identification, we show that these genes have many characters in common with experimentally identified essential genes. They should then be regarded as truly essential genes.     

Solution structure of a tobacco lipid transfer protein exhibiting new biophysical and biological features

Plant lipid transfer proteins are small soluble extracellular proteins that are able to bind and transfer a variety of lipids in vitro. Recently, it has been proposed that lipid transfer proteins may play a key role in plant defence mechanisms, especially during the induction of systemic acquired resistance. However, very little is known about the proteins expressed in developing plants and tissues, since almost all the biophysical and structural data available to date on lipid transfer proteins originate from proteins present in storage tissues of monocot cereal seeds. In this paper, we report the structural and functional characteristics of a lipid transfer protein (named LTP1_1) constitutively expressed in young aerial organs of Nicotiana tabacum (common tobacco). The unlabelled and uniformly labelled proteins were produced in the yeast Pichia pastoris, and we determined the three-dimensional (3D) structure of LTP1_1 using nuclear magnetic resonance (NMR) spectroscopy and molecular modeling techniques. The global fold of LTP1_1 is very close to the previously published structures of LTP1 extracted from cereal seeds, including an internal cavity. However, the chemical shift variations of several NMR signals upon lipid binding show that tobacco LTP1_1 is able to bind only one LysoMyristoylPhosphatidylCholine (LMPC), while wheat and maize LTPs can bind either one or two. Titration experiments using intrinsic tyrosine fluorescence confirm this result not only with LMPC but also with two fatty acids. These differences can be explained by the presence in tobacco LTP1_1 of a hydrophobic cluster closing the second possible access to the protein cavity. This result suggests that LTP1 lipid binding properties could be modulated by subtle changes in a conserved global structure. The biological significance of this finding is discussed in the light of the signalling properties of the tobacco LTP1_1-jasmonate complex described elsewhere.     

Universal biases in protein composition of model prokaryotes

The levels of cellular organization in living organisms are the results of a variety of selection pressures. We have investigated here the final outcome of this integrated selective process in proteins of the best known microbial models Escherichia coli, Bacillus subtilis, and Methanococcus jannaschii, supposed to have undergone separate evolution for more than 1 billion years. Using multivariate analysis methods, including correspondence analysis, we studied the overall amino acid composition of all proteins making a proteome. Starting from and further developing previous results that had pointed out some general forces driving the amino acid composition of the proteomes of these model bacteria, we explored the correlations existing between the structure and functions of the proteins forming a proteome and their amino acid composition. The electric charge of amino acids measured against hydrophobicity creates a highly homogeneous cluster, made exclusively of proteins that are core components of the cytoplasmic membrane of the cell (integral inner membrane proteins). A second bias is imposed by the G+C content of the genome, indicating that protein functions are so robust with respect to amino acid changes that they can accommodate a large shift in the nucleotide content of the genome. A remarkable role of aromatic amino acids was uncovered. Expressed orphan proteins are enriched in these residues, suggesting that they might participate in a process of gain of function during evolution.