Expression of dnaK and groESL operons during sporulation of Bacillus megaterium

Expression of the dnaK and groEL genes during sporulation was assayed by determination of their mRNA levels by Northern blotting and compared with the relative level and rate of synthesis of the corresponding proteins. The ability of sporulating cells to respond to a heat shock by an increase in dnaK and groEL expression was determined at the same time. Synthesis of DnaK and GroEL encoding mRNAs during sporulation in non-shocked cells was low suggesting that this kind of cytodifferentiation was not accompanied by enhanced synthesis of these chaperones. Also the ability of sporulating cells to respond to a heat shock by stimulating their synthesis substantially decreased during the reversible and dropped to negligible values during the irreversible sporulation phase. Nevertheless, some dependence of the heat shock response on sporulation exists because sporulation suppression by mutation or by netropsin treatment further decreased the cells' capacity to respond to a heat shock.     

Changes in ffh, uvrA, groES and dnaK mRNA Abundance as a Function of Acid-Adaptation and Growth Phase in Bifidobacterium longum BBMN68 Isolated from Healthy Centenarians

The acid adaption is commonly used as a strategy to enhance the acid tolerance of bifidobacteria. However, the acid tolerance response (ATR) mechanism elicited by this method is unclear. Real-time relative-quantitative PCR was applied to analyze the changes in the expressions of ffh, uvrA, groES, and dnaK involved in the ATR after acid-adaptation in Bifidobacterium longum BBMN68 in different growth phases. BBMN68 was cultured at a constant neutral pH during the whole growth phase. Without acid-adaptation, the survival ratios at the lethal pH 3.0 were 0.25% and 17% in the exponential and stationary phases, respectively. The genes ffh, uvrA, groES, and dnaK were significantly higher in the stationary phase than in the exponential phase. The results indicated that although there was no acid stress, the acid tolerance of cells was elevated from the exponential phase into stationary phase. After acid-adaptation at pH 5.0 for 120 min, the survival ratios of BBMN68 in the exponential and stationary phases were increased to 2.5 and 31%, respectively. In the exponential phase, ffh, uvrA groES, and dnaK were significantly decreased after acid-adaptation. In the stationary phase, after acid-adaptation for 15, 60, and 120 min, the genes uvrA, groES, and dnaK were significantly decreased, whereas, ffh was significantly up-regulated at 15 min, and then suppressed at 60 and 120 min after acid-adaptation. The results represented that the ATR in B. longum was different from other bacteria, and ffh may be the transient acid gene.     

Abscisic acid-regulated Glb1 transient expression in cultured maize P3377 cells

In a study of the 5′-flanking sequence of the Zea mays L. (maize) Glb1 gene in vitro, serial promoter deletions were generated and linked with the β-glucuronidase (GUS) reporter gene. The promoter deletion-GUS fusions were introduced into the maize P3377 cell line by particle bombardment. GUS assays indicated that treatment of the maize cultured cells with abscisic acid (ABA) was required for Glb1-driven GUS transient expression, and that the –272-bp sequence of the Glb1 promoter was sufficient for ABA-regulated expression of GUS. The longest undeleted sequence used, –1391 GUS, showed relatively low expression which could be indicative of an upstream silencer element in the Glb1 promoter between –1391 and –805. Further studies show that the Glb1-driven GUS activity of bombarded maize P3377 cells increases with increasing ABA concentration (up to 100–300 μm). Site-directed mutagenesis of a putative ABA response element, Em1a, abolished GUS expression in P3377 cells. This observation indicated that the Em1a sequence in the Glb1 5′ regulatory region is responsible for the positive ABA regulation of gene expression. Received: 9 May 1997 / Revision received: 9 November 1997 / Accepted: 8 December 1997     

mRNA translation in yeast during entry into stationary phase

The expression of some Saccharomyces cerevisiae genes is induced as cells enter stationary phase. Their mRNAs are translated during a period in the growth cycle when the translational apparatus is relatively inert, thereby raising the possibility that these mRNAs compete effectively for a limiting pool of translation factors. To test this idea, the translation of mRNAs carrying different 5′-leaders was compared during exponential growth and after entry into stationary phase upon glucose starvation. Closely related sets of lacZ mRNAs, carrying 5′-leaders from the PYK1, PGK1, RpL3, Rp29, HSP12, HSP26 or THI4 mRNAs, were studied. These mRNAs displayed differing translational efficiencies during exponential growth, but their relative translatabilities were not significantly affected by entry into stationary phase, indicating that they compete just as effectively under these conditions. Polysome analysis revealed that the wild-type PYK1, ACT1 and HSP26 mRNAs are all translated efficiently during stationary phase, when the translational apparatus is relatively inert. Also, significant levels of the translation initiation factors eIF-2α, eIF-4E and eIF-4A were maintained during the growth cycle. These data are consistent with the idea that, while translational activity decreases dramatically during entry into stationary phase, yeast cells maintain excess translational capacity under these conditions. Received: 31 March 1998 / Accepted: 4 May 1998     

One-step transformation of the dimorphic yeast Yarrowia lipolytica

An efficient one-step transformation method for the dimorphic yeast Yarrowia lipolytica is described. Using cells grown overnight on agar plates, the whole process is carried out within 1 h. The transformant clones could be recovered on selective plates as early as 36–48 h after plating. The efficiency was better than 10⁵ transformants/μg replicative plasmid DNA. Effects of cell density, dithiothreitol, heat shock, poly(ethylene glycol) 4000 concentration and the wetness of selective plates were investigated. Received: 17 February 1997 / Received revision: 4 April 1997 / Accepted: 19 April 1997     

Characterization of a Cell Membrane-Associated Proteinase from Lactobacillus helveticus CRL 581

The production of a proteinase from Lactobacillus helveticus CRL 581 was studied. The highest specific activity was found at the early exponential growth phase of cells cultured in milk. The lowest levels of proteinase were detected in MRS broth, while in the casein–yeast extract–glucose broth enzyme production increased gradually during the fermentation and reached maximal values at the stationary phase. The proteinase, found to be associated with the cell membrane fraction, hydrolyzed β-casein more rapidly than α-casein. The enzyme was not released from washed cells in the presence or absence of calcium, which suggests that the enzyme did not undergo self-digestion. Received: 28 January 1997 / Accepted: 8 March 1997