Characteristic electron microscopical projections of the small ribosomal subunit from Thermomyces lanuginosus

Inflammatory Thermophilic Fungi are Used in Biotechnology Applications

Thermophilic microorganisms which can colonize at extreme ecological niches are known as extremophiles. Because of their capacity to withstand high temperatures, enzymes from these organisms are relatively heat stable. The versatile enzyme properties of these organisms make them excellent candidates in biotechnology. In general, fungi have been widely used for the production of proteins and enzymes, since they can grow rapidly in a low cost media and they secrete proteins into the extra-cellular medium. Recently, these organisms have also been used in large scale fermentation as host for the expression of heterologous proteins in industrial applications. However, little is known about the regulation and genetic manipulations of these fungi. We have previously shown the regulation of gene expression in a thermophilic fungus, Thermyces lanuginosus, using an inducible invertase system. The aim of this review is to elucidate the recent advances of thermophilic fungi, and their implications in industrial applications are discussed.

Structures of small subunit ribosomal RNAs in situ from Escherichia coli and Thermomyces lanuginosus

Small ribosomal subunits from the prokaryote Escherichia coli and the eukaryote Thermomyces lanuginosus were imaged electron spectroscopically, and single particle analysis used to yield three-dimensional reconstructions of the net phosphorus distribution representing the nucleic acid (RNA) backbone. This direct approach showed both ribosomal RNAs to have a three domain structure and other characteristic morphological features. The eukaryotic small ribosomal subunit had a prominent bill present in the head domain, while the prokaryotic subunit had a small vestigial bill. Both ribosomal subunits contained a thick 'collar' central domain which correlates to the site of the evolutionarily conserved ribosomal RNA core, and the location of the majority of ribosomal RNA bases that have been implicated in translation. The reconstruction of the prokaryotic subunit had a prominent protrusion extending from the collar, forming a channel approximately 1.5 nm wide and potentially representing a 'bridge' to the large subunit in the intact monosome. The basal domain of the prokaryotic ribosomal subunit was protein free. In this region of the eukaryotic subunit, there were two basal lobes composed of ribosomal RNA, consistent with previous hypotheses that this is a site for the 'non-conserved core' ribosomal RNA.

Ribosomal proteins of Thermomyces lanuginosus--characterisation by two-dimensional gel electrophoresis and differential disassembly

One- and two-dimensional gel electrophoresis were employed to characterise the proteins derived from the ribosomes of the thermophilic fungus Thermomyces lanuginosus. Approximately 32 (29 basic and 3 acidic) and 45 (43 basic and 2 acidic) protein spots were resolved from Th. lanuginosus small and large ribosomal subunits, respectively. The molecular weight of the small subunit proteins ranged from 9,800-36,000 Da with a number average molecular weight of 20,300 Da. The molecular weight range for the large subunit proteins was 12,000-48,500 Da with a number average molecular weight of 25,900 Da. Most proteins appeared to be present in unimolar amounts. These data are comparable with but not identical to those from other eukaryotic ribosomes. The sensitivities of the ribosomal proteins to increasing concentrations of NH4Cl were also evaluated by two-dimensional gel electrophoresis. Most ribosomal proteins were gradually released over a wide range of salt concentrations but some were preferentially enriched in one or two salt conditions.

Electron microscopic visualisation of the 5S rRNA-YL3 complex from Saccharomyces cerevisiae

The complex comprising 5S ribosomal RNA and the ribosomal protein YL3 (5S rRNP) was isolated from yeast (Saccharomyces cerevisiae), and positively contrasted preparations were imaged by transmission electron microscopy. The overall dimensions of the 5S rRNP complex in the micrographs were 10 nm by 6 nm. Three predominant projections were selected from several hundred putative particles for digitisation and computer averaging to yield two-dimensional constructions with reproducible spatial resolutions exceeding 2 nm. The enhanced projection images were compatible with structural models of this complex based on biochemical studies.

Electron microscopical projections of the large ribosomal subunit from Thermomyces lanuginosus

Multivariate statistical analysis and hierarchical ascendant classification have been used to construct averages of two fundamental electron microscopical views of large ribosomal subunits from the thermophilic fungus Thermomyces lanuginosus. The first was roughly pentagonal in shape and corresponded to the canonical crown view seen in images of large subunits from prokaryotic species. The second and more prevalent projection was elliptical in shape, and by matching protuberances could be interpreted as the complex rotated from the crown orientation. Because of its ubiquity and consistency, this elongated view could potentially serve as the standard for structural comparisons of the large ribosomal subunit from eukaryotic organisms, and as the basis for a three-dimensional reconstruction.