Detection of the homology among proteins by immunochemical cross-reactivity between denatured antigens. Application to the threonine and methionine regulated aspartokinases-homoserine dehydrogenases from Escherichia coli K 12.

The two isofunctional enzymes aspartokinases-homoserine dehydrogenases I and II from Escherichia coli K 12 are compared using immunochemical techniques. The antibodies raised against one of these two proteins when in its native state can only recognize the homologous antigen, whether it is native or denatured. Contrarily, the antibodies raised against one of these two proteins when in its denatured state can recognize both the homologous and heterologous denatured antigens. The existence of this cross-reaction only between the two denatured aspartokinases-homoserine dehydrogenases suggests that these two enzymes have some similarity since such a reaction is not detected with several other denatured proteins. The regions involved in this similarity are buried inside the native proteins, and become exposed only upon denaturation. The same results, the existence of a cross-reaction between denatured species and none between the native ones, is obtained with proteolytic fragments derived from these two proteins and endowed with homoserine dehydrogenase activity. This resemblance between the two aspartokinases-homoserine dehydrogenases suggests that these proteins derive from a common ancestor. It is also proposed that such a cross-reaction between two denatured proteins is evidence for an homology between their amino acid sequences, and that the use of denatured proteins as both immunogens and antigens could be useful in detecting sequence homologies.     

Responses of heather moorland and Mediterranean mouflon foraging to prescribed-burning and cutting

We assessed the effects of prescribed burning and cutting on mouflon (Ovis gmelini musimon × Ovis sp.) spring habitat using an experimental design (17.28 ha) of 2 burned, 2 cut, and 2 untreated plots within a homogeneous stand dominated by heather (Erica cinerea and Calluna vulgaris). Overall, we found a shift in treated plots from ligneous species to herbaceous species with high digestive and energetic values for mouflon. We also found a consistently higher number of mouflon feeding on these treated habitats compared to untreated plots. Such effects were still apparent 4 years after habitat modifications. Our approaches could be used by managers to improve and maintain the range of mouflon populations experiencing habitat loss (e.g., woody plant encroachment) and for which the condition of an animal has often a high economical value through trophy hunting. © 2011 The Wildlife Society.     

Microbiome Influences Prenatal and Adult Microglia in a Sex-Specific Manner

1. Download high-res image (242KB)
2. Download full-size image

     

Amiloride does not alter NaCl avoidance in Fischer-344 rats

Fischer-344 (F-344) rats differ from other common rat strains in that they fail to show any preference for NaCl at any concentration in two- bottle preference tests. Because 100 microM amiloride partially blocks the NaCl-evoked chorda tympani (CT) response in electrophysiological studies, we tested NaCl preference (0.068-0.273 M) in F-344 rats with and without 100 microM amiloride solution as the solvent. A third group was tested with unadulterated NaCl solutions following CT transection. Amiloride had no significant effect on the NaCl preference-aversion function, whereas CT transection significantly reduced NaCl avoidance. These results suggest that the amiloride-sensitive component of the NaCl response is not necessary for F-344 rats to display avoidance of NaCl, but the entire CT input is.      

Stepwise inactivation of Escherichia coli aspartokinase-homoserine dehydrogenase I

In the range of guanidine hydrochloride concentrations from 0.2 to 1.2 M, aspartokinase-homoserine dehydrogenase I loses its enzymatic properties, both kinase and dehydrogenase activities and their allosteric inhibition by L-threonine. Ligands which stabilize the tetrameric native structure protect the enzyme against inactivation. Under some conditions, all the functional properties do not disappear at the same rate: an intermediate species possessing only the kinase activity can be detected. Several arguments suggest that this partly active intermediate has a monomeric structure. These results show that deactivation of aspartokinase-homoserine dehydrogenase I is a stepwise process, compatible with the reverse of the previously described reactivation [Garel, J.-R., & Dautry-Varsat, A. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 3379-3383]. The same measurements performed with a monofunctional fragment carrying the dehydrogenase activity show that the loss of dehydrogenase activity is the same whether or not the polypeptide chain is intact or lacks the kinase region; this finding suggests that the protein is composed of independent regions. The influence of protein aggregation in studying unfolding-refolding of oligomeric enzymes is also discussed.     

Molecular biodiversity of cassava begomoviruses in Tanzania: evolution of cassava geminiviruses in Africa and evidence for East Africa being a center of diversity of cassava geminiviruses

Cassava is infected by numerous geminiviruses in Africa and India that cause devastating losses to poor farmers. We here describe the molecular diversity of seven representative cassava mosaic geminiviruses (CMGs) infecting cassava from multiple locations in Tanzania. We report for the first time the presence of two isolates in East Africa: (EACMCV-[TZ1] and EACMCV-[TZ7]) of the species East African cassava mosaic Cameroon virus, originally described in West Africa. The complete nucleotide sequence of EACMCV-[TZ1] DNA-A and DNA-B components shared a high overall sequence identity to EACMCV-[CM] components (92% and 84%). The EACMCV-[TZ1] and -[TZ7] genomic components have recombinations in the same genome regions reported in EACMCV-[CM], but they also have additional recombinations in both components. Evidence from sequence analysis suggests that the two strains have the same ancient origin and are not recent introductions. EACMCV-[TZ1] occurred widely in the southern part of the country. Four other CMG isolates were identified: two were close to the EACMV-Kenya strain (named EACMV-[KE/TZT] and EACMV-[KE/TZM] with 96% sequence identity); one isolate, TZ10, had 98% homology to EACMV-UG2Svr and was named EACMV-UG2 [TZ10]; and finally one isolate was 95% identical to EACMV-[TZ] and named EACMV-[TZ/YV]. One isolate of African cassava mosaic virus with 97% sequence identity with other isolates of ACMV was named ACMV-[TZ]. It represents the first ACMV isolate from Tanzania to be sequenced. The molecular variability of CMGs was also evaluated using partial B component nucleotide sequences of 13 EACMV isolates from Tanzania. Using the sequences of all CMGs currently available, we have shown the presence of a number of putative recombination fragments that are more prominent in all components of EACMV than in ACMV. This new knowledge about the molecular CMG diversity in East Africa, and in Tanzania in particular, has led us to hypothesize about the probable importance of this part of Africa as a source of diversity and evolutionary change both during the early stages of the relationship between CMGs and cassava and in more recent times. The existence of multiple CMG isolates with high DNA genome diversity in Tanzania and the molecular forces behind this diversity pose a threat to cassava production throughout the African continent.     

PhySIC_IST: cleaning source trees to infer more informative supertrees

Background  

Supertree methods combine phylogenies with overlapping sets of taxa into a larger one. Topological conflicts frequently arise among source trees for methodological or biological reasons, such as long branch attraction, lateral gene transfers, gene duplication/loss or deep gene coalescence. When topological conflicts occur among source trees, liberal methods infer supertrees containing the most frequent alternative, while veto methods infer supertrees not contradicting any source tree, i.e. discard all conflicting resolutions. When the source trees host a significant number of topological conflicts or have a small taxon overlap, supertree methods of both kinds can propose poorly resolved, hence uninformative, supertrees.