A versatile modular vector set for optimizing protein expression among bacterial, yeast, insect and mammalian hosts.

We have developed a unified, versatile vector set for expression of recombinant proteins, fit for use in any bacterial, yeast, insect or mammalian cell host. The advantage of this system is its versatility at the vector level, achieved by the introduction of a novel expression cassette. This cassette contains a unified multi-cloning site, affinity tags, protease cleavable linkers, an optional secretion signal, and common restriction endonuclease sites at key positions. This way, genes of interest and all elements of the cassette can be switched freely among the vectors, using restriction digestion and ligation without the need of polymerase chain reaction (PCR). This vector set allows rapid protein expression screening of various hosts and affinity tags. The reason behind this approach was that it is difficult to predict which expression host and which affinity tag will lead to functional expression. The new system is based on four optimized and frequently used expression systems (Escherichia coli pET, the yeast Pichia pastoris, pVL and pIEx for Spodoptera frugiperda insect cells and pLEXm based mammalian systems), which were modified as described above. The resulting vector set was named pONE series. We have successfully applied the pONE vector set for expression of the following human proteins: the tumour suppressor RASSF1A and the protein kinases Aurora A and LIMK1. Finally, we used it to express the large multidomain protein, Rho-associated protein kinase 2 (ROCK2, 164 kDa) and demonstrated that the yeast Pichia pastoris reproducibly expresses the large ROCK2 kinase with identical activity to the insect cell produced counterpart. To our knowledge this is among the largest proteins ever expressed in yeast. This demonstrates that the cost-effective yeast system can match and replace the industry-standard insect cell expression system even for large and complex mammalian proteins. These experiments demonstrate the applicability of our pONE vector set.

Qualitative and quantitative characterization of autophagy in Caenorhabditis elegans by electron microscopy.

Caenorhabditis elegans has been introduced relatively late into the field of autophagy with no previous results by classical methods. Therefore, it has to be studied in parallel with both traditional electron microscopy and modern molecular approaches. In general, correct identification of autophagic elements by electron microscopy is indispensable to establish a firm basis for our understanding of the process. The principles and the method for identification, applied also for C. elegans, are summarized first in this article, to facilitate their utilization both for further studies and the analysis of new cell types and to support researchers new to electron microscopy techniques. Studying autophagy in the worm by electron microscopy has required the development of special handling and sampling techniques in addition to overcoming the general technical difficulties due to the nature of C. elegans samples. These are described in detail, together with some initial qualitative and quantitative results obtained by them. The feasibility of the presented method is supported by data which show that in continuously fed worms the autophagic compartment is in the lower range of the 10(-2)% order of magnitude of the cytoplasmic volume, while immediately after molting or upon starvation in the second larval period, usually more than a 10-fold increase can be measured. In dauer larvae, individual variation of the autophagic compartment is very high. The predauer stage in daf-2 mutants does not seem to show significant constitutive autophagic activity. Some autophagy-related gene mutants show characteristic ultrastuctural features, such as autophagosomes with membrane abnormalities (unc-51/Atg1) or the hypertrophy of multivesicular bodies (let-512/Vps34, bec-1/Atg6).