Walls of the mycelial (M) and yeast-like (Y) forms of Mucor rouxii were prepared with the carbohydrate labelled with 14C and the peptide and polypeptide labelled with SH. Walls were extracted by sequential treatment with EDTA, NaOH and acetic acid. The polymers released were separated by glass-fibre paper electrophoresis and gel filtration which showed the presence, in both M and Y walls, of high molecular weight strongly acidic polysaccharides, high molecular weight weakly acidic glycoproteins and low molecular weight glycopeptides, which are weakly acidic or neutral. The strongly acidic polysaccharides from both M and Y forms contained D-glucuronic acid, D-mannose, D-galactose and L-fucose ; the glycoproteins and glycopeptides from both forms had D-mannose as the major sugar. Y walls gave in addition a weakly acidic polysaccharide containing D-glucuronic acid and D-mannose. The strongly acidic polysaccharides of the M form contained a greater proportion of D-galactose and L-fucose than did corresponding polymers of the Y form. The differences in composition of these polymers are discussed in terms of the possible differences in their structure and the relationship to morphology.

The relationship between genetically different seed sizes and seedling survival under severe nutrient deprivation was determined by comparing ten inbred lines of Arabidopsis thaliana. Seedlings were supplied with only sterile distilled water, and the number of days between germination and death (complete chlorosis) was recorded. Seedlings from genotypes with larger seeds survived longer than seedlings from genotypes with smaller seeds. These results suggest a genetically based adaptive significance of larger seed size resulting from a greater seedling tolerance of nutrient deprivation. This may confer a potentially important selective advantage when nutrient deprivation is the result of a low resource supply in the environment, or the result of nutrient depletion by neighbors.

No abstract

The Tat (twin-arginine translocation) system is a protein targeting pathway utilized by prokaryotes and chloroplasts. Tat substrates are produced with distinctive N-terminal signal peptides and are translocated as fully folded proteins. In Escherichia coli, Tat-dependent proteins often contain redox cofactors that must be loaded before translocation. Trimethylamine N-oxide reductase (TorA) is a model bacterial Tat substrate and is a molybdenum cofactor-dependent enzyme. Co-ordination of cofactor loading and translocation of TorA is directed by the TorD protein, which is a cytoplasmic chaperone known to interact physically with the TorA signal peptide. In the present study, a pre-export TorAD complex has been characterized using biochemical and biophysical techniques, including SAXS (small-angle X-ray scattering). A stable, cofactor-free TorAD complex was isolated, which revealed a 1:1 binding stoichiometry. Surprisingly, a TorAD complex with similar architecture can be isolated in the complete absence of the 39-residue TorA signal peptide. The present study demonstrates that two high-affinity binding sites for TorD are present on TorA, and that a single TorD protein binds both of those simultaneously. Further characterization suggested that the C-terminal ‘Domain IV’ of TorA remained solvent-exposed in the cofactor-free pre-export TorAD complex. It is possible that correct folding of Domain IV upon cofactor loading is the trigger for TorD release and subsequent export of TorA.

No abstract