The methylotrophic yeast Pichia pastoris has gained widespread acceptance as a system of choice for heterologous protein expression in part because of the simplicity of techniques required for its molecular genetic manipulation (1). Several different procedures are available for introducing DNA into P. pastoris-spheroplast generation (2), electroporation (3), alkali cation (3,4), or polyethylene glycol (PEG) treatment (5). Here we describe a condensed protocol for cell preparation and transformation that works reliably with either auxotrophic markers or antibiotic selection.The introduction of exogenous DNA into an organism requires two steps: (i) the preparation of competent cells for DNA uptake and (ii) the transformation of the cells with the DNA. Transformation of P. pastoris by electroporation is a quick procedure. However, preparation of conventional electroporation-competent cells requires hours of work involving several washes, incubations, and centrifugations. In contrast, competent cell preparation for the heatshock method is short, but transformation requires approximately 2 h (4). The heat-shock procedure gives approximately 100-fold lower transformation efficiency than electroporation with plasmids containing auxotrophic marker genes such as HIS4. Additionally, the selection of zeocin-resistant transformants using the heat-shock transformation protocol does not work reliably.We have modified the preparation of competent cells from the heat-shock procedure (5) and combined it with transformation by electroporation (3) to yield a condensed protocol that works consistently with auxotrophic markers or antibiotic selection. The main modification of the heat-shock procedure is the addition of a step in which P. pastoris cells are incubated in an optimized concentration of dithiothreitol (DTT). The cells prepared by this "hybrid" method are then electroporated using the same parameters as conventional electroporation.Transformation efficiencies using the condensed protocol are comparable to the conventional electroporation procedure using auxotrophic markers but are approximately 20-fold lower using the zeocin resistance marker. However, the condensed protocol provides sufficient transformants, including multicopy integrants, for protein expression studies and has several advantages over the conventional electroporation and heat-shock methods. Table 1 compares the steps in cell preparation and transformation for conventional electroporation, heat shock, and our condensed protocol. Compared to the heat-shock method, the condensed protocol requires less time for the transformation step and provides much higher transformation efficiencies. Compared to the electroporation procedure, the new procedure saves both reagents

The methylotrophic yeast, Pichia pastoris, has been genetically engineered to produce many heterologous proteins for industrial and research purposes. In order to secrete proteins for easier purification from the extracellular medium, the coding sequence of recombinant proteins are initially fused to the Saccharomyces cerevisiae α-mating factor secretion signal leader. Extensive site-directed mutagenesis of the prepro region of the α-mating factor secretion signal sequence was performed in order to determine the effects of various deletions and substitutions on expression. Though some mutations clearly dampened protein expression, deletion of amino acids 57-70, corresponding to the predicted 3rd alpha helix of α-mating factor secretion signal, increased secretion of reporter proteins horseradish peroxidase and lipase at least 50% in small-scale cultures. These findings raise the possibility that the secretory efficiency of the leader can be further enhanced in the future.

Spider silk is renowned for its extraordinary mechanical properties, having a balance of high tensile strength and extensibility. To date, the majority of studies have focused on the production of dragline silks from synthetic spider silk gene products. Here we report the first mechanical analysis of synthetic egg case silk fibers spun from the Latrodectus hesperus tubuliform silk proteins, TuSp1 and ECP-2. We provide evidence that recombinant ECP-2 proteins can be spun into fibers that display mechanical properties similar to other synthetic spider silks. We also demonstrate that silks spun from recombinant thioredoxin-TuSp1 fusion proteins that contain the conserved C-terminal domain exhibit increased extensibility and toughness when compared to the identical fibers spun from fusion proteins lacking the C-terminus. Mechanical analyses reveal that the properties of synthetic tubuliform silks can be modulated by altering the postspin draw ratios of the fibers. Fibers subject to increased draw ratios showed elevated tensile strength and decreased extensibility but maintained constant toughness. Wide-angle X-ray diffraction studies indicate that postdrawn fibers containing the C-terminal domain of TuSp1 have more amorphous content when compared to fibers lacking the C-terminus. Taken together, these studies demonstrate that recombinant tubuliform spidroins that contain the conserved C-terminal domain with embedded protein tags can be effectively spun into fibers, resulting in similar tensile strength but increased extensibility relative to nontagged recombinant dragline silk proteins spun from equivalently sized proteins.

The methylotrophic yeast, Pichia pastoris, is widely used as a host organism for the expression of heterologous proteins. Currently, the Zeocin and blasticidin resistance genes are the only dominant selectable markers that can be used for primary selection of transformants. In this report we describe new expression vectors that can be used to select directly for P. pastoris transformants using G418 resistance conferred by a modified Tn903kan r gene. Compared to other dominant markers, this system is more economical and offers a higher transformation efficiency, due to the small sizes of the cloning vectors, pKAN B and pKANα B (GenBank Accession Nos EU285585 and EU285586, respectively). Additionally, multicopy transformants can be generated using these new vectors.

Although Pichia pastoris is a popular protein expression system, it exhibits limitations in its ability to secrete heterologous proteins. Therefore, a REMI (restriction enzyme mediated insertion) strategy was utilized to select mutant beta-galactosidase supersecretion (bgs) strains that secreted increased levels of a β-galactosidase reporter.Many of the twelve BGS genes may have functions in intracellular signaling or vesicle transport. Several of these strains also appeared to contain a more permeable cell wall. Preliminary characterization of four bgs mutants showed that they differed in the ability to enhance the export of other reporter proteins. bgs13, which has a disruption in a gene homologous to Saccharomyces cerevisiae protein kinase C(PKC1), gave enhanced secretion ofmost recombinant proteins that were tested, raising the possibility that it has the universal super-secreter phenotype needed in an industrial production strain of P. pastoris.