Foreign transcriptional enhancers in yeast. II. Interplay of the polyomavirus transcriptional enhancer and Saccharomyces cerevisiae promoter elements

Presence of protein production enhancers results in significantly higher methanol-induced protein production in Pichia pastoris

Background

The yeast Komagataella phaffii, better known as Pichia pastoris, is a commonly used host for recombinant protein production. Here expression vectors are reported that address the different steps of the transcription–translation–secretion pathway of heterologous protein production.

Results

Transcription and translation enhancing elements were introduced in an expression cassette for the production of recombinant Aspergillus niger feruloyl esterase A. The yield was increased by threefold as compared to the yield without these elements. Multiple copy strains were selected using a zeocin resistance marker in the expression cassette and showed another sixfold higher yield. Modification of the C-terminal amino acid sequence of the secretion signal did not significantly improve the production yield. Similar data were obtained for the production of another protein, recombinant human interleukin 8. Upscaling to fed-batch fermentation conditions resulted in a twofold increase for reference strains, while for strains with enhancing elements a tenfold improvement was observed.

Conclusions

Pichia pastoris is used for recombinant protein production in industrial fermentations. By addressing the transcription and translation of mRNA coding for recombinant protein, significant yield improvement was obtained. The yield improvement obtained under microscale conditions was maintained under fed-batch fermentation conditions. These data demonstrate the potential of these expression vectors for large scale application as improved production of proteins has major implications on the economics and sustainability of biocatalyst dependent production processes e.g. for the production of pharmaceuticals and for the bioconversions of complex molecules.

The Saccharomyces cerevisiae ARG4 initiator of meiotic gene conversion and its associated double-strand DNA breaks can be inhibited by transcriptional interference

In the yeast Saccharomyces cerevisiae, as in other eukaryotes, some regions of the genome have a much higher level of meiotic gene conversion than others. Previous deletion analysis indicated that the sequence necessary for the high level of gene conversion within the ARG4 region defined an initiation site located between positions -316 and -37 [relative to the first base pair (+1) of the ARG4 coding sequence] of the ARG4 promoter. To test whether this sequence is sufficient to promote gene conversion in a novel chromosomal context, we inverted on the chromosome various DNA fragments including the implicated region and the ARG4 coding sequence. Surprisingly, these inversions resulted in the loss of the normal recombination properties and double-strand-break formation associated with this process. By Northern analysis, we found that a transcript traverses the ARG4 initiation site in these inversion mutants but not in the wild type. When transcription through this region was prevented by a transcription terminator, the activity of the initiation site and the formation of double-strand breaks were restored. From these results and from complementary deletion analysis in the normal ARG4 orientation, we conclude that the activity of the ARG4 initiation site requires protection from transcriptional interference.