The promoter of filamentation (POF1) protein from <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> is an ATPase involved in the protein quality control process

Background

The gene YCL047C, which has been renamed promoter of filamentation gene (POF1), has recently been described as a cell component involved in yeast filamentous growth. The objective of this work is to understand the molecular and biological function of this gene.

Results

Here, we report that the protein encoded by the POF1 gene, Pof1p, is an ATPase that may be part of the Saccharomyces cerevisiae protein quality control pathway. According to the results, Δpof1 cells showed increased sensitivity to hydrogen peroxide, tert-butyl hydroperoxide, heat shock and protein unfolding agents, such as dithiothreitol and tunicamycin. Besides, the overexpression of POF1 suppressed the sensitivity of Δpct1, a strain that lacks a gene that encodes a phosphocholine cytidylyltransferase, to heat shock. In vitro analysis showed, however, that the purified Pof1p enzyme had no cytidylyltransferase activity but does have ATPase activity, with catalytic efficiency comparable to other ATPases involved in endoplasmic reticulum-associated degradation of proteins (ERAD). Supporting these findings, co-immunoprecipitation experiments showed a physical interaction between Pof1p and Ubc7p (an ubiquitin conjugating enzyme) in vivo.

Conclusions

Taken together, the results strongly suggest that the biological function of Pof1p is related to the regulation of protein degradation.

     

Phylogenetic relationship of zeins and coixins as determined by immunological cross-reactivity and Southern blot analysis

Zeins from Zea mays L cv. Maya and coixins from Coix lacryma-jobi L. cv. Adlay were fractionated to obtain -, -, and -zein and -, -, and -coixin. The -coixins were composed of 4 polypeptide classes of 27 kDa (C1), 25 kDa (C2), 17 kDa (C4) and 15 kDa (C5) with solubility properties very similar to those of the 22 kDa and 19 kDa -zeins. Like the -zeins, the C1 and C2 -coixins corresponded to 80% of total Coix prolamins. The fraction corresponding to -coixin contained only one protein band of 22 kDa (C3). This coixin fraction has solubility properties similar to those of -zein and represents 15% of the total coixin. The -zein fraction was composed of a major 17 kDa protein band, while the -coixin fraction consisted of a mixture of - and -coixins.Polyclonal antibodies raised against C1 recognized C1 and C2 and cross-reacted strongly with the 22 kDa -zein, as did C4 and C5 antisera. The antiserum against -coixin showed strong cross-reaction with -zein. The homology between coixins and zeins was further investigated by using Southern hybridization analyses. The genomic DNA of maize and Coix were digested with several restriction enzymes and probed with cDNA clones representing 19 and 22 kDa -zeins as well as the 28 and 16 kDa -zeins. The Coix genome showed complex cross-hybridization sequences with the 22 kDa -zein cDNA, while no cross-hybridization was observed with the 19 kDa cDNA clone. The cDNA clone representing the 28 kDa -zein cross-hybridized with only one band of Coix genomic DNA, in contrast to the three bands observed in maize. This same Coix sequence also cross-hybridized with the cDNA clone representing the 16 kDa -zein. The relevance of these findings are discussed in the context of the origin of zein and coixin genes.     

Selective expression of a major allergen and cytotoxin, Asp f I, in Aspergillus fumigatus. Implications for the immunopathogenesis of Aspergillus-related diseases.

Asp f I is a major 18-kDa Aspergillus fumigatus allergen and a member of the mitogillin family of cytotoxins. The nucleotide sequence of the Asp f I gene was determined by sequencing polymerase chain reaction products amplified from A. fumigatus spore DNA. The entire 678-bp DNA includes an 81-bp leader sequence, preceding the N-terminal alanine codon, a 52-bp intron, and a 444-bp open reading frame, encoding a 149-amino acid protein (M(r) 16,899), which is 99% homologous to mitogillin from Aspergillus restrictus. A mAb-based ELISA was used to compare Asp f I levels in spores, mycelia, and culture filtrate, and to determine the kinetics of allergen production. Disrupted hyphae or spore extracts had a 1000-fold lower level of Asp f I than culture filtrate, suggesting that germination of spores and growth of the fungus are essential for allergen production. Asp f I levels in A. fumigatus and A. restrictus peaked at day 3 (0.87 to 12.1 micrograms/ml), however, the allergen was not detected in Aspergillus flavus, Aspergillus niger, Aspergillus terreus, and Aspergillus nidulans cultures (< 1.5 ng/ml) on either days 3 or 8. Northern analysis confirmed that Asp f I mRNA was detected only in A. fumigatus and A. restrictus, but not in the other four Aspergillus spp. Asp f I-specific DNA was generated after polymerase chain reaction amplification of genomic mycelial DNA obtained from A. fumigatus and A. restrictus, but not from the other Aspergillus spp. The results show that Asp f I is selectively expressed in A. fumigatus, and suggest that this cytotoxin could be a specific virulence factor for A. fumigatus.     

A review of recent immunochemical studies ofBlomia tropicalis andEuroglyphus maynei allergens

Exposure to mites other thanDermatophagoides spp., particularlyBlomia tropicalis andEuroglyphus maynei, has been increasingly recognized as a cause of asthma. Positive skin tests and serum IgE antibodies toB. tropicalis have been reported in asthmatic patients from several areas of the world, including São Paulo (Brazil), Hong Kong and Tampa (Florida, USA). Analysis ofB. tropicalis extracts showed undetectable levels of the major Group I and Group IIDermatophagoides spp. allergens. Immunoabsorption experiments showed that most of the IgE antibodies toB. tropicalis ( 70%) reacted with species-specific allergens. Murine monoclonal antibodies toB. tropicalis could present antigens that were recognized by human IgG antibodies. Sensitization toE. maynei has been reported in Europe, North and South America and Australia. Analysis of four differentE. maynei extracts by ELISA and RIA showed thatE. maynei produces an allergen that is antigenically related toDermatophagoides Group I allergens. The amino acid sequence of this allergen (Eur m I) has recently been reported. Further identification and purification ofB. tropicalis andE. maynei allergens is required to develop specific assays for measuring these allergens in dust samples. This will make it possible to investigate the relationship between exposure toB. tropicalis orE. maynei and the development of sensitization and allergic disease.     

Seasonal flooding,topography, and organic debris interact to influence the emergence and distribution of seedlings in a tropical grassland

In seasonally flooded wetlands, inundation and associated organic debris deposition followed by a drawdown period can promote plant community diversity across space and time. Post‐flood regeneration might be influenced by the direct effect of flooding on seed dispersal and seedling emergence, as well as the indirect effect of organic debris on seed trapping and germination. Our objective was to examine the influence of seasonal flooding, topography, and organic debris cover on seedling distribution in a seasonally flooded grassland. We measured species richness, seedling abundance, and organic debris cover for 3 yr in a seasonally flooded grassland in the Pantanal, Brazil, at three topographic levels at the end of the flood season and during the dry season when there was no debris deposition. A total of 43 species were recorded, with no difference in species richness detected between seasons. However, the abundance of some species was higher post‐flood than during the dry period. The greatest seedling abundance and richness were found post‐flood at intermediate elevations, followed by high and the lowest elevations. Seed germination and seedling establishment were likely suppressed at low topographic positions due to shading from organic debris and poor drainage. Therefore, areas with predictable annual floods promote diversity by creating spatial and temporal variations in environmental conditions.     

Satellite DNA repeat sequence variation is low in three species of burying beetles in the genus Nicrophorus (Coleoptera: Silphidae)

Three satellite DNA families were identified in three species of burying beetles, Nicrophorus orbicollis, N. marginatus, and N. americanus. Southern hybridization and nucleotide sequence analysis of individual randomly cloned repeats shows that these satellite DNA families are highly abundant in the genome, are composed of unique repeats, and are species-specific. The repeats do not have identifiable core elements or substructures that are similar in all three families, and most interspecific sequence similarity is confined to homopolymeric runs of A and T. Satellite DNA from N. marginatus and N. americanus show single-base-pair indels among repeats, but single-nucleotide substitutions characterize most of the repeat variability. Although the repeat units are of similar lengths (342, 350, and 354 bp) and A + T composition (65%, 71%, and 71%, respectively), the average nucleotide divergence among sequenced repeats is very low (0.18%, 1.22%, and 0.71%, respectively). Transition/transversion ratios from the consensus sequence are 0.20, 0.69, and 0.70, respectively.