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Journal Highlights

Prokaryote Intelligence: An Oxymoron No Longer?

Tommassen

Bacteria adapt to many fluctuating environmental conditions using two-component regulatory systems, which usually consist of a sensor in the cytoplasmic membrane and a cytoplasmic response activator. A group from the Netherlands shows, in the case of such a phosphate-sensing system in E. coli, that the bacterium "learns" to react more quickly to phosphate poor-conditions. This happens, the researchers show, because the naive bacterium has few sensor and response activator proteins, but it responds to phosphate starvation by making more, and these are remarkably stable. PI Jan Tommassen, of the University of Utrecht, the Netherlands, says that there is evidence for crosstalk among some environmental regulatory systems, and that "this might be the basis for the existence within a prokaryotic cell of a phospho-neural network." (See Current Topics, p. 495.)

(S. M. Hoffer, H. V. Westerhoff, K. J. Hellingwerf, P. W. Postma, and J. Tommassen. 2001. Autoamplification of a two-component regulatory system results in "learning" behavior. J. Bacteriol. 183:4914-4917.) Abstract | Full Text

Stability Control in [gb]-Globin Assembly

Russell and Yu

Eukaryotic mRNA half-lives range from several minutes to several days. It is not surprising that mRNAs encoding cytokines, proto-oncogenes, and factors that regulate gene transcription, cell growth, and cell cycling are generally short-lived, while mRNAs encoding structural proteins or highly abundant functional products, such as globins, are long-lived.

Using in vitro methods and transgenic approaches, Jia Yu and J. Eric Russell of the University of Pennsylvania, Philadelphia, show that ß-globin mRNA assembles an mRNP complex similar to one important for stabilizing the human ß-globin mRNA. "Moreover, we have identified a candidate 3' UTR sequence where this mRNP complex is likely to assemble," says Russell. "Our findings indicate that the high stabilities of the human a-globin and ß-globin mRNAs may be regulated through a shared mechanism. Therapeutic manipulation of such a system might benefit individuals with a- or ß-thalassemias, which are common congenital disorders characterized by imbalanced expression of the a- and ß-globin proteins. We are engaged in identifying the number and precise location of 3' UTR sequences that assemble ß-globin mRNP complexes, as well as defining the trans-acting factors that participate in assembly."

(J. Yu and J. E. Russell. 2001. Structural and functional analysis of an mRNP complex that mediates the high stability of human ß-globin mRNA. Mol. Cell. Biol. 21:5879-5888.) Abstract | Full Text

Proteomics Rules!

Jungblut

Genomics outshines proteomics in the scientific consciousness because many journals won't publish incomplete proteome analyses, says Peter R. Jungblut, of the Max Planck Institute for Infection Biology, Berlin. But completeness in proteome analysis is well-nigh impossible, he says. Yet, proteomics offers a more accurate window on function, and indeed on the genome itself. Case in point: in this paper, using proteomics, Jungblut and others reveal six proteins not predicted by genomics in a culture of M. tuberculosis. They used a combination of two-dimensional electrophoresis, matrix-assisted laser desorption ionization, and nano-electrospray mass spectrometry. "Proteome analysis gives a view into the real functional situation of a biological system and contributes even to the completeness of genomes," says Jungblut. "Therefore, completeness should not be a criterion to discriminate against proteome studies."

(P. R. Jungblut, E.-C. Muller, J. Mattow, and S. H. E. Kaufmann. 2001. Proteomics reveals open reading frames in Mycobacterium tuberculosis H37Rv not predicted by genomics. Infect. Immun. 69:5912-5914.) 

Transgenic Clover to Cover Cattle Against Pneumonic Pasteurellosis

Lo

Bovine pneumonic pasteurellosis caused by Mannheimia haemolytica is a major expense for the cattle industry. Immunizing cattle by needle injection is stressful for cattle, and labor intensive. Reggie Lo and colleagues of the University of Guelph, Ontario, are developing an oral vaccine by producing the antigenic domains of leukotoxin (Lkt), the most protective antigen, of M. haemolytica in transgenic clover. The transgenic antigen was stable in dried leaves at room temperature for several days. "This is important for production of a vaccine requiring no refrigeration and suitable for mixing with regular feed," says Lo. "The next phase is to vaccinate animals by feeding the transgenic clover to cattle and utilizing the ruminating activity of the animals to deliver the vaccine to the tonsils."

"Such a vaccine will be inexpensive to prepare and will require minimal processing and storage and essentially no labor cost," says Lo.

(R. W. H. Lee, J. Strommer, D. Hodgins, P. E. Shewen, Y. Niu, and R. Y. C. Lo. 2001. Towards Development of an edible vaccine against bovine pneumonic pasteurellosis using transgenic white clover expressing a Mannheimia haemolytica A1 Leukotoxin 50 fusion protein. Infect. Immun. 69:5786-5793.) Abstract | Full Text

Mapping Control of Virulence in Yersinia

Type III secretion systems represent a common pathogenic tool of many gram-negative bacteria. Upon bacterial contact with host cells, type III machines deliver protein toxins across the eukaryotic plasma membrane. Once inside the cell, these proteins manipulate host signal transduction pathways, resulting in rearrangement of the cytoskeleton and induction of an apoptotic program.

Olaf Schneewind, then of the University of California, and colleagues show in Yersinia enterocolitica that four signals are necessary to induce type III secretion. "Our research suggests that the signals act on pathways that relieve repressors," says Schneewind. "Bear in mind, without the pathway the bacterium is avirulent, so if you knew how to interfere you could prevent infection.

"Now that we know the signals and the repressors, we are going to try to find the genes that act on the pathways," says Schneewind.

(V. T. Lee, S. K. Mazmanian, and O. Scheewind. 2001. A program of Yersinia enterocolitica type III secretion reactions is activated by specific signals. J. Bacteriol. 183:4970-4978.) Abstract | Full Text

Temp-Sensitive Plasmids Make Better Mutator Strains for Building Better Industrial Microbes

Schellenberger

Recent advances in genomics and protein evolution have dramatically improved our ability to introduce novel catalytic functions or entire metabolic pathways into microorganisms. However, industrial use of such engineered strains is often constrained by their limited tolerance to the high concentrations of metabolites and solvents required for efficient production of biomaterials. More robust strains frequently must be generated by random mutagenesis and selection. This directed evolution can be accelerated in mutator strains, which carry defects in DNA repair genes, but following that, the normal low mutation rate must be restored.

Mutator strains are hard to use due to genetic instability. Now Volker Schellenberger and colleagues of Genencor International, Inc., Palo Alto, Calif., have constructed temperature-sensitive plasmids that temporarily increase the mutation frequency of their hosts by 20- to 4,000-fold. "Two rounds of selection were sufficient to increase the tolerance of E. coli to dimethylformamide by 20 g/liter," says Schellenberger.

(O. Selifonova, F. Valle, and V. Schellenberger. 2001. Rapid evolution of novel traits in microorganisms. Appl. Environ. Microbiol. 67:3645-3649.) Abstract | Full Text