- Volume 140, Issue 9, 1994

The existence of more than one chitin synthetase in fungal cells poses the question of whether these enzymes have similar or different localization. The subcellular distribution of chitin synthetases 1 and 2 (Chs1 and Chs2) was determined in cell-free extracts of Saccharomyces cerevisiae fractionated by sucrose density gradient sedimentation. Chs1 was examined in two strains: ATCC 26109, a wild-type strain, and D3C (MATα ura3-52). Chs2 was investigated in a strain (D3B) freed of Chs1 by gene disruption (MATa his4 ura3-52 chs1::URA3). A prolonged, strong centrifugation (20 h at 265000 g) was necessary to cleanly resolve two major populations of chitin synthetase particles: chitosomes (a population of microvesicles of low buoyant density, d = 1.15 g ml-1) and plasma membrane (a population of vesicles of high buoyant density, d = 1.21 g ml-1). Chs1 and Chs2 were both present in chitosomes and plasma membrane, but the relative distribution of each chitin synthetase in these two membranous populations varied. Chs2 was much less abundant than Chs1 and required Co2+rather than Mg2+as a cofactor. A salient finding was the high sensitivity of chitosomal Chs2 to high centrifugal forces. The subcellular distribution of 1,3-β-glucan synthetase was the same in the three strains studied, i.e. unaffected by the presence or absence of Chs1. Culture conditions affected the profiles of chitin and glucan synthetases: the relative abundance of Chs1 in chitosomes or plasma membrane was quite different in cells grown on two different media but the buoyant density was not affected; in contrast, there was shift in the buoyant density of the two peaks of 1,3-β-glucan synthetase. We concluded that the subcellular localization of Chs1 and Chs2 remains the same despite genetic and other differences in the properties of these enzymes. We confirmed that 1,3-β-glucan synthetase and chitin synthetase exhibit a partially different subcellular distribution-an indication that these two enzymes are mobilized through different secretory pathways.

A systematic evaluation of the in vitro (1,3)-β-glucan synthase assay parameters was performed using microsomes prepared from Candida albicans from either yeast or mycelial phase cells. Enzyme activities of both yeast and mycelial phase microsomes depended on the presence of guanosine-5′-O-(3-thiophosphate) and either bovine serum albumin or a detergent [W-1 (polyoxyethylene ether detergent) or Brij-35 (polyoxyethylene ether, 23 lauryl ether)]. Brij-35 was included in standard assays as it was compatible with the permeabilized whole-cell assay. Microsomes derived from both the yeast and mycelial phases generally yielded similar glucan synthase activities under a range of different assay conditions. Brij-35 significantly stabilized the enzyme, yielding a half-life of 5.6 d at 4 °C, compared with 0.9 d without detergent. The addition of detergent during mechanical breakage of yeast cells dramatically improved glucan synthase stability and activity. Enzyme catalysis was linear for at least 75 min with 100 μg protein from microsomes of yeast cells grown to mid-exponential phase, with an apparent K m for UDP-glucose of 1.1 mM. The pH and temperature optima were 7.75 and 30 °C, respectively. Glucan synthase activity was highest in cells derived from early mid-exponential phase and declined to a basal level by stationary phase. A permeabilization-based in situ assay for glucan synthase was developed. Cells were permeabilized with 2% (v/v) solution of toluene/methanol (1:1) and assayed for glucan synthase activity using standard reaction mixtures. Reactions were linear for 30 min and were inhibited by known inhibitors of glucan synthesis. This study represents the first characterization of glucan synthase using yeast and mycelial phase microsomes and adaptation of a permeabilized system using a single C. albicans strain with standardized assay conditions.

Colicin V is a ribosomally synthesized antimicrobial peptide produced by Escherichia coli. Four recently characterized genes, arranged in two convergent operons on the plasmid pColV-K30, are required for colicin V synthesis, export and immunity. We report the purification and N-terminal amino acid sequencing of the colicin V protein. Our results demonstrate that the colicin V primary translation product, which consists of 103 amino acids, is proteolytically processed. A leader peptide, consisting of 15 amino acid residues, is removed from the N-terminus during maturation of colicin V. This leader peptide is not related to the N-terminal signal sequences which direct proteins across the cytoplasmic membrane via the Sec pathway. The molecular mass of colicin V, obtained by mass spectrometry analysis, showed that the peptide consists of only unmodified amino acids. The deduced amino acid sequence of the leader peptide was highly homologous to the N-terminal extensions found in non-lantibiotic, peptide bacteriocins produced by Gram-positive bacteria. These findings strongly indicate that colicin V belongs to a family of small peptide bacteriocins that have been found previously only among the Gram-positive lactic acid bacteria.

The hydrolysis of soluble starch, raw starch and pullulan with recombinant glucoamylase P from Hormoconis resinae was competitively inhibited by β-cyclodextrin with apparent K i values of 190 μM, 13 μM and 1.4 μM, respectively. Inhibition of dextran hydrolysis was partial: a maximum inhibition of 22% was achieved with a dextran concentration of 0.3 × K m and up to 4 mM β-cyclodextrin. Hydrolysis of short oligosaccharides was not inhibited by β-cyclodextrin at levels up to 20 mM. The enzyme bound to raw starch at pH 4.3 and 4 °C with an association constant of 3.4 × 105M-1. Sequence alignment studies showed raw-starch-binding consensus amino acids in the C-terminal part of glucoamylase P. Partial hydrolysis with papain resulted in degradation of deglycosylated glucoamylase P into three fragments of 53, 51 and 14 kDa, respectively, as estimated by SDS-PAGE. The amino-terminal sequences of the 51 and 53 kDa fragments were identical with that of native glucoamylase P. The amino terminus of the 14 kDa fragment (Ser-Ser-X-Gln-Val-Ser-), corresponded to the sequence starting at residue 474 of intact glucoamylase P. Kinetic measurements of truncated glucoamylase P showed changes in the K m values of larger polysaccharides, but no changes in K cat values compared to the intact enzyme. It was concluded that glucoamylase P contains a catalytic core domain and a raw-starch-binding domain involved in inhibition of polysaccharide hydrolysis by β-cyclodextrin.

Sexual agglutination, caused by agglutination substance (AS) on a and α cell walls, is the first indispensable step of the mating reaction in ascosporogenous yeasts including Saccharomyces cerevisiae. The AS biosynthetic process in S. cerevisiae was investigated by pulse label-chase experiments with analysis by polyacrylamide gel electrophoresis (PAGE) for 16 h in the presence of urea. Because of its low mobility, AS can be separated from other proteins by prolonged PAGE. Nascent AS was integrated into cell walls after it linked covalently to a ‘carrier’ glycoprotein. The results suggest that the ‘carrier’ is synthesized stepwise through three distinct precursors (III → II → I). The ‘carrier’ glycoprotein (I) and its precursors (II, III) were synthesized in both a, α haploid and a/α diploid cells. The N-glycosylation linkage inhibitor, tunicamycin, and protein synthesis inhibitor, puromycin, inhibited the III to I maturation. The results indicated that both the ‘carrier’ and the nascent active site of AS linked to the ‘carrier’ are integrated into the wall in a haploid cell while the ‘carrier’ alone is integrated in a diploid cell.

Immunogold preparations of Escherichia coli, using anti-GyrA and anti-GyrB antibodies to the subunits of DNA gyrase, showed clear labelling with both secondary antibody and protein A-gold conjugates. Both proteins were located mainly in the cytoplasm, with typically less than 10% in the nucleoid. This partitioning of gyrase proteins between nucleoid and cytoplasm was non-random and was consistently observed for a range of different cell preparations. Total gold particle counts were highly variable but suggested levels of at least 1000-3000 molecules per cell for both GyrA and GyrB. Sequential treatment with both anti-GyrA and anti-GyrB monoclonal antibodies resulted in simultaneous labelling of both proteins and revealed no clear association between the two groups of molecules. Treatment of cells with chloramphenicol caused marked changes in nucleoid conformation, but no reduction in cytoplasmic labelling of gyrase proteins. On the assumption that gyrase complexes within the nucleoid are not differentially masked from the monoclonal antibodies, the results obtained in this study suggest that most of the gyrase proteins are not associated with either central nucleoid DNA or cytoplasmic loops of peripheral single-stranded DNA, but are distributed randomly throughout the cytoplasm.

Pyrolysis mass spectrometry (PYMS) and PCR using arbitrary primers were used to characterize strains of Bradyrhizobium japonicum isolated from fields in northern Italy. The combination of techniques allowed us to identify bacteria derived from inoculants and to demonstrate that information about the nature of one inoculant was incorrect. PYMS also indicated that the derivatives from one inoculant formed two distinct populations: one like the parent strain and the other altered phenotypically.

The nucleotide sequence of the Leuconostoc lactis 533 cryptic plasmid pCI411 (2926 bp) was determined. Analysis revealed the presence of three open reading frames (ORFs). ORF 1 was capable of encoding a 24.9 kDa peptide which shared homology with the replication initiation protein (RepB) from a number of Gram-positive rolling circle plasmids. ORF 2 could encode a peptide of 6.6 kDa which was homologous to the RepC protein of the lactococcal plasmid pWV01. A function could not be assigned to ORF 3, which was capable of encoding a 12.1 kDa peptide. Transcription—translation analysis indicated the presence of three peptides of the predicted molecular masses. A putative double strand origin of replication (DSO) was identified which showed strong similarity with the DSO of a number of Gram-positive plasmids including pE194 from Staphylococcus. Structural analysis identified a number of direct and indirect repeats in addition to putative recombination-specific sites (RSA and RSB) in the non-coding region of pCI411. The observed characteristics suggest that this plasmid replicates using the rolling circle mechanism. pCI411, which could be introduced into Leuconostoc, Lactococcus, Streptococcus, Lactobacillus and Bacillus is the first plasmid from the genus Leuconostoc to be characterized in such detail.

The linear plasmid pPZG101 of Streptomyces rimosus R6 was restriction mapped with the enzymes Asel, Bfrl, Dral and Xbal. It is 387 kb in size and the ends are inverted repeats of at least 95 kb in length. Twenty spontaneous morphological variants and seventeen auxotrophic mutants were screened for changes in the plasmid. Two strains were found that had lost all plasmid sequences. Four strains had integrated parts of the plasmid into the chromosome. Restriction analysis suggested that at least three of the integrated strains had retained free plasmid ends. If it is assumed that the chromosome of S. rimosus R6 is linear, this might be explained by replacement of one or both chromosome ends by a plasmid end. One strain, which overproduced oxytetracycline, carried an enlarged linear plasmid of 1 Mb in size that had acquired chromosomal sequences from the oxytetracycline biosynthesis cluster.

Five of the genes known to encode the synthesis of poly(glycerol phosphate), the major teichoic acid of Bacillus subtilis 168, are organized in two divergently transcribed operons (a divergon), denoted tagAB and tagDEF. To monitor their expression, the 399 bp intergenic region separating the first structural genes of these operons was fused, in both orientations, to a lacZ reporter gene, allowing measurement of promoter activity under specific physiological conditions. Under all experimental conditions, tagA and tagD appeared coordinately expressed, the level of tagD being always higher than that of tagA. No influence of the chromosomal context was observed. Phosphate limitation was accompanied by reduced tag gene expression. Following the onset of sporulation, expression of tag genes diminished rapidly and was essentially abolished by stage II. During germination, the activity of tag genes was detectable before the rise in culture turbidity associated with spore outgrowth. In contrast to tagC (dinC), the expression of which is DNA-damage-inducible, the induction of SOS functions had no effect on tagA and tagD gene expression. The biological significance of these results is discussed.

The role of a 20 bp conserved region located 45-64 nucleotides 5′ of the spoVA transcription start point in Bacillus subtilis and Bacillus licheniformis was investigated by deletion analysis and by mobility shift assay. Deletions 5′ of this conserved sequence had little effect on expression of a spoVA-lacZ fusion, whereas deletions extending into the sequence reduced expression of the spoVA-lacZ fusion by 85%. The timing of expression of spoVA was not affected by deletion of the sequence. The region was shown by mobility shift assays to bind specifically to a protein. Binding activity was detected in protein extracts prepared from bacteria 1 h or more after they had started to sporulate, but not in extracts prepared from vegetative bacteria. Mutations in all known spoO loci were screened but none prevented appearance of the binding activity; nor did mutations in any of the stage II and III loci tested. It is concluded that the 20 bp conserved region is the binding site of an activator that is subject to temporal regulation independent of known spo loci.