Yeast

About: Yeast is a research topic. Over the lifetime, 31777 publications have been published within this topic receiving 868967 citations. The topic is also known as: yeasts.

Increased amounts of HMG-CoA reductase induce "karmellae": a proliferation of stacked membrane pairs surrounding the yeast nucleus.

Abstract: Overproduction of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in yeast resulted in striking morphological effects on the structure of intracellular membranes. Specifically, stacks of paired membranes closely associated with the nuclear envelope were observed in strains that over-produced the HMG1 isozyme, one of two isozymes for HMG-CoA reductase in yeast. These nuclear-associated, paired membranes have been named "karmellae." In strains that overproduced the HMG1 isozyme, HMG-CoA reductase was present in the karmellar layers. At mitosis, karmellae were asymmetrically segregated: the mother cells inherited all of the karmellae and the daughter cells inherited none. A membranous structure of different morphology was occasionally found in cells that overproduced the HMG2 isozyme. These observations further establish the existence of cellular mechanisms that monitor the levels of membrane proteins and compensate for changes in these levels by inducing synthesis of particular types of membrane.

Amino-terminal protein processing in Saccharomyces cerevisiae is an essential function that requires two distinct methionine aminopeptidases

Abstract: We previously characterized a methionine aminopeptidase (EC 3.4.11.18; Met-AP1; also called peptidase M) in Saccharomyces cerevisiae, which differs from its prokaryotic homologues in that it (i) contains an N-terminal zinc-finger domain and (ii) does not produce lethality when disrupted, although it does slow growth dramatically; it is encoded by a gene called MAP1. Here we describe a second methionine aminopeptidase (Met-AP2) in S. cerevisiae, encoded by MAP2, which was cloned as a suppressor of the slow-growth phenotype of the map1 null strain. The DNA sequence of MAP2 encodes a protein of 421 amino acids that shows 22% identity with the sequence of yeast Met-AP1. Surprisingly, comparison with sequences in the GenBank data base showed that the product of MAP2 has even greater homology (55% identity) with rat p67, which was characterized as an initiation factor 2-associated protein but not yet shown to have Met-AP activity. Transformants of map1 null cells expressing MAP2 in a high-copy-number plasmid contained 3- to 12-fold increases in Met-AP activity on different peptide substrates. The epitope-tagged suppressor gene product was purified by immunoaffinity chromatography and shown to contain Met-AP activity. To evaluate the physiological significance of Met-AP2, the MAP2 gene was deleted from wild-type and map1 null yeast strains. The map2 null strain, like the map1 null strain, is viable but with a slower growth rate. The map1, map2 double-null strains are nonviable. Thus, removal of N-terminal methionine is an essential function in yeast, as in prokaryotes, but yeast require two methionine aminopeptidases to provide the essential function which can only be partially provided by Met-AP1 or Met-AP2 alone.

Influence of environment on the content and composition of microbial free amino acid pools.

Abstract: SUMMARY: The free amino acid pool contents of Gram-negative bacteria (Aerobacter aerogenes, Erwinia carotovora, Pseudomonas fluorescens) were studied as functions of the growth environment and were compared with those from correspondingly grown cultures of Gram-positive bacteria (Bacillus subtilis var. niger, B. megaterium, B. polymyxa) and the yeast Saccharomyces cerevisiae. Although the pools of the Gram-positive bacteria and the yeast contained five to 20 times the concentration of free amino acids present in the pools of Gram-negative bacteria, all pools were similar in containing only a limited range of detectable amino acids. Glutamate invariably predominated and generally accounted for over 50% of the total amino acid content of the pool. The contents and composition of pools from micro-organisms maintained in steady states in chemostat cultures did not vary with time, but changed significantly with changes in either growth rate or the nature of the growth limitation. However, these pool variations were small compared with those resulting from addition of 2% (w/v) NaCl to a culture of growing bacteria. With cultures of Gram-negative bacteria, sudden changes in medium salinity effected marked and rapid changes in free glutamate content; with Gram-positive bacteria, similar changes occurred, but extremely slowly. Addition of 4% (w/v) NaCl to growing yeast cultures brought about no observed changes in pool size or composition. These results are discussed with reference to the involvement of free amino acids in synthesis and functioning of microorganisms.

Glycerol overproduction by engineered saccharomyces cerevisiae wine yeast strains leads to substantial changes in By-product formation and to a stimulation of fermentation rate in stationary phase

Abstract: Six commercial wine yeast strains and three nonindustrial strains (two laboratory strains and one haploid strain derived from a wine yeast strain) were engineered to produce large amounts of glycerol with a lower ethanol yield. Overexpression of the GPD1 gene, encoding a glycerol-3-phosphate dehydrogenase, resulted in a 1.5- to 2.5-fold increase in glycerol production and a slight decrease in ethanol formation under conditions simulating wine fermentation. All the strains overexpressing GPD1 produced a larger amount of succinate and acetate, with marked differences in the level of these compounds between industrial and nonindustrial engineered strains. Acetoin and 2,3-butanediol formation was enhanced with significant variation between strains and in relation to the level of glycerol produced. Wine strains overproducing glycerol at moderate levels (12 to 18 g/liter) reduced acetoin almost completely to 2,3-butanediol. A lower biomass concentration was attained by GPD1-overexpressing strains, probably due to high acetaldehyde production during the growth phase. Despite the reduction in cell numbers, complete sugar exhaustion was achieved during fermentation in a sugar-rich medium. Surprisingly, the engineered wine yeast strains exhibited a significant increase in the fermentation rate in the stationary phase, which reduced the time of fermentation.