The genetics of nuclear pre-mRNA splicing: a complex story

The occurrence of introns in nuclear precursor RNAs (pre-mRNAs) is widespread in eukaryotes, and the splicing process that removes them is basically the same in yeasts as it is in higher eukaryotes. Splicing takes place in a very large, multi-component complex, the spliceosome, and biochemical studies have been complicated by the large number of splicing factors involved. This review describes how genetic approaches used to study RNA splicing inSaccharomyces cerevisiae have complemented the biochemical studies and led to rapid advances in the field.     

Protein translocation as a tool: The current rapamycin story

In cell biology and pharmacology, small chemicals are mostly used as agonists and antagonists against receptors and enzymes. The immunosuppressant rapamycin can serve an entirely different purpose: if employed sensibly, it might function as an inducer of dimerization that is able to rapidly activate enzyme activity inside the intact cell. A number of very recent developments such as photoactivatable derivatives make rapamycin an even more attractive tool for basic science.     

The osmotic gradient in kidney medulla: a retold story

This article is an attempt to simplify lecturing about the osmotic gradient in the kidney medulla. In the model presented, the kidneys are described as a limited space with a positive interstitial hydrostatic pressure. Traffic of water, sodium, and urea is described in levels (or horizons) of different osmolarity, governed by osmotic forces and positive interstitial pressure. In this way, actions of the countercurrent multiplier in nephron tubules and of the countercurrent exchanger in vasa recta are integrated in each horizon. We hope that this approach can help students to better accept conventional presentations in their textbooks.     

Respiratory poliomyelitis: a follow-up study.

Data from the medical records of 113 patients living in Manitoba who had contracted respiratory poliomyelitis between 1952 and 1959 were compared with information obtained from interviews with these patients in 1980. The study was designed to determine whether the patients'' respiratory function, mobility, ability to perform daily tasks, and employment, residential and marital status had changed between 1 year after the onset of polio and 1980. The patients'' dependence on mechanical aids and other people was also studied. More than half (56%) of the patients perceived their respiratory impairment to be the same as it was 1 year after the onset of polio, 27% perceived the impairment to be increased, and 17% perceived it to be decreased. There was an association between level of respiratory function, mobility and ability to perform daily tasks. The 69 patients who lived at home had better respiratory function, mobility and ability to perform daily tasks than the 24 patients who were assisted by a home care program and the 20 who lived in hospital. The latter group had the lowest levels of respiratory and functional ability.     

The unfolding story of a redox chaperone

Oxidative stress, especially in combination with heat stress, poses a life-threatening challenge to many organisms by causing protein misfolding and aggregation. In this issue, Reichmann et al. demonstrate how a destabilized linker region of the bacterial chaperone Hsp33 prevents aggregation of a denatured protein by stabilizing structural elements.     

The two sides of a lipid-protein story

Protein–membrane interactions play essential roles in a variety of cell functions such as signaling, membrane trafficking, and transport. Membrane-recruited cytosolic proteins that interact transiently and interfacially with lipid bilayers perform several of those functions. Experimental techniques capable of probing changes on the structural dynamics of this weak association are surprisingly limited. Among such techniques, electron spin resonance (ESR) has the enormous advantage of providing valuable local information from both membrane and protein perspectives by using intrinsic paramagnetic probes in metalloproteins or by attaching nitroxide spin labels to proteins and lipids. In this review, we discuss the power of ESR to unravel relevant structural and functional details of lipid–peripheral membrane protein interactions with special emphasis on local changes of specific regions of the protein and/or the lipids. First, we show how ESR can be used to investigate the direct interaction between a protein and a particular lipid, illustrating the case of lipid binding into a hydrophobic pocket of chlorocatechol 1,2-dioxygenase, a non-heme iron enzyme responsible for catabolism of aromatic compounds that are industrially released in the environment. In the second case, we show the effects of GPI-anchored tissue-nonspecific alkaline phosphatase, a protein that plays a crucial role in skeletal mineralization, and on the ordering and dynamics of lipid acyl chains. Then, switching to the protein perspective, we analyze the interaction with model membranes of the brain fatty acid binding protein, the major actor in the reversible binding and transport of hydrophobic ligands such as long-chain, saturated, or unsaturated fatty acids. Finally, we conclude by discussing how both lipid and protein views can be associated to address a common question regarding the molecular mechanism by which dihydroorotate dehydrogenase, an essential enzyme for the de novo synthesis of pyrimidine nucleotides, and how it fishes out membrane-embedded quinones to perform its function.     

The cell biology of autophagy in metazoans: a developing story

The cell biological phenomenon of autophagy (or ;self-eating') has attracted increasing attention in recent years. In this review, we first address the cell biological functions of autophagy, and then discuss recent insights into the role of autophagy in animal development, particularly in C. elegans, Drosophila and mouse. Work in these and other model systems has also provided evidence for the involvement of autophagy in disease processes, such as neurodegeneration, tumorigenesis, pathogenic infection and aging. Insights gained from investigating the functions of autophagy in normal development should increase our understanding of its roles in human disease and its potential as a target for therapeutic intervention.     

Rainforest rehabilitation on a productive Macadamia property: The Brockley story

A transformed rainforest remnant is visible from the main road, but even more impressive changes can be found deep within the privately owned agricultural property. This story, told by the landholders and regeneration team member, recounts the processes and outcomes of an 8-year program to restore remnants and convert extensive weedy linkages to regrowth rainforest.     

Autophagy by ARF: a short story

In this issue of Molecular Cell, Reef et al. (2006) describe a shortened unstable form of the ARF tumor suppressor protein that localizes within mitochondria, where it reduces membrane potential and triggers autophagy. Could this account for the Mdm2- and p53-independent tumor suppressive effects of ARF?     

GSK3: a SHAGGY frog story

Glycogen synthase kinase 3 was discovered in mammals several years ago but only recently has it become clear that this enzyme is acutely regulated by hormones such as insulin and by growth factors. In mammals, it appears to be controlled by a signalling pathway linked to phosphoinositide 3-kinase and may regulate a range of biosynthetic processes. Evidence is now accumulating that GSK3 plays a key role in the regulation of cell fate and differentiation in many eukaryotic species.     

Cytochromes P450: a success story

Cytochrome P450 proteins, named for the absorption band at 450 nm of their carbon-monoxide-bound form, are one of the largest superfamilies of enzyme proteins. The P450 genes (also called CYP) are found in the genomes of virtually all organisms, but their number has exploded in plants. Their amino-acid sequences are extremely diverse, with levels of identity as low as 16% in some cases, but their structural fold has remained the same throughout evolution. P450s are heme-thiolate proteins; their most conserved structural features are related to heme binding and common catalytic properties, the major feature being a completely conserved cysteine serving as fifth (axial) ligand to the heme iron. Canonical P450s use electrons from NAD(P)H to catalyze activation of molecular oxygen, leading to regiospecific and stereospecific oxidative attack of a plethora of substrates. The reactions carried out by P450s, though often hydroxylation, can be extremely diverse and sometimes surprising. They contribute to vital processes such as carbon source assimilation, biosynthesis of hormones and of structural components of living organisms, and also carcinogenesis and degradation of xenobiotics. In plants, chemical defense seems to be a major reason for P450 diversification. In prokaryotes, P450s are soluble proteins. In eukaryotes, they are usually bound to the endoplasmic reticulum or inner mitochondrial membranes. The electron carrier proteins used for conveying reducing equivalents from NAD(P)H differ with subcellular localization. P450 enzymes catalyze many reactions that are important in drug metabolism or that have practical applications in industry; their economic impact is therefore considerable.