Abstract:
Brewing yeast strains are usually aneuploid or polyploid with no true mating type. Thus
many of the techniques which can be used to genetically modify laboratory yeast strains
cannot be
applied to them. This study was aimed at developing the technology for the
genetic modification of brewing yeasts towards producing genetically improved brewing
strains, suitable for use in large scale beer production.
A
system has been developed which can produce brewing yeast transformants with high
genetic stability and unimpaired brewing performance. Such transformants contain only the
required extra genetic material and no superfluous vector DNA. This system has also been
demonstrated to have
potential for the genetic labelling of yeast strains as a means of
accurate identification which could also be used towards the
patent protection of commercially
important yeast strains. _
A method for the stabilisation of
heterologous proteins produced in yeast has been
investigated. The hypothesis that the glycosylation of heterologous proteins can improve their
stability in yeast was tested by mutating the Escherichia coli ß-lactamase gene to produce
N-linked
glycosylation substrates. Two of the modified proteins were glycosylated when
expressed in yeast, one of which had improved thermal stability.
A wheat
11-amylase gene yeast expression cassette has been constructed using the
wheat secretion
signal and yeast gene control sequences. Expression of the cassette in
yeast results in efficient starch-degrading activity both in liquid and on solid media. The
enzyme is efficíently secreted and approximately 90% of the activity is found in yeast culture
supernatants.
