Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The yeast Saccharomyces cerevisiae is able to sense and respond to changes in its
immediate environment. Information regarding the nutritional status of the
extracellular environment is sensed by membrane receptor systems and relayed
through signalling pathways to the nuclear interior, affecting the transcription of
specific genes., Transcription factors, which function downstream of these signal
transduction pathways, have to be transported into the nucleus after synthesis in the
cytoplasm in order to regulate transcriptional events. Transport into the nucleus
occurs in a tightly regulated manner at the nuclear pore complex, which is located in
the nuclear membrane, and requires the recognition of transport signal sequences,
which are present in the proteins that are to be transported. Signalling pathways
control the nuclear accessibility of transcriptional regulators by modifying their
respective signal sequences.
In response to a limited availability of carbon or nitrogen, cells are able to change
their morphology from a unicellular ovoid form to elongated cells attached to each
other. This morphological change is associated with daughter cells that remain
attached to their respective mother cells following unipolar budding, thus forming
filamentous structures referred to as pseudohyphae. The regulation of the
development of pseudohyphae is correlated with other physiological processes, such
as starch degradation and the invasion of agar-containing media. Mss11p performs a
central role in the regulation of the genes required for these processes and it has
been shown to specifically regulate the expression of FL011, which encodes a cell
surface protein critical for pseudohyphal development, and STA2, which encodes an
extracellular glucoamylase functioning in the degradation of starch.
The aim of this study was to characterise the functioning of Mss11p.
Overexpression analysis indicates that Mss11p functions as an inducer of invasive
growth, cell elongation and flocculation. Furthermore, MSS11 deletion improves
biomass formation and suppresses the growth defect of yeast from a L:1278b genetic
background transformed with the RAS2val19 allele on non-fermentable carbon
sources. Biochemical analysis shows that Mss11p is a nuclear protein of
approximately 97 kDa in apparent size that is maintained at relatively low levels in
yeast. Finally, the data suggest a model in which Mss11p functions as a mediator of
the transcriptional regulation of various genes. / AFRIKAANSE OPSOMMING: Die gis Saccharomyces cerevisiae is in staat om veranderinge in sy onmiddelike
omgewing waar te neem en daarop te reageer. Inligting betreffende die
beskikbaarheid van voedingstowwe in die omgewing word vanaf membraan
reseptorsisteme deur middel van seintransduksiekaskades na die nukleus herlei,
waar die transkripsie van spesifieke gene beïnvloed word. Transkripsie faktore wat
stroom af van hierdie seintransduksie funksioneer, moet na die nukleus vervoer word
na vervaardiging in die sitoplasma, om sodoende transkripsionele gebeurtenisse te
reguleer. Die vervoer van faktore na die binnekant van die nukleus vind onder streng
regulering plaas by die nukleêre porie kompleks, wat in die nukleêre membraan
gesitueer is. Vervoer vind plaas deur middel van die herkenning van nukleêre
lokaliseringsekwense wat in die proteïene wat vervoer word, teenwoordig is.
Seintransduksiekaskades beheer die beskikbaarheid van proteïene tot die nukleus
deur hulonderskeidelike nukleêre lokaliseringsekwense te modifiseer.
Selle is in staat om hul morfologie te verander van 'n eensellige eliptiese vorm tot
verlengde selle wat aan mekaar geheg bly in reaksie op die beperkende
beskikbaarheid van koolstof of stikstof bronne. Hierdie morfologiese verandering
word geassosieer met dogterselle wat ná monopolêre botselvorming aan hul
moederselle geheg bly, en dus filamentagtige strukture vorm wat pseudohifes
genoem word. Die regulering van die ontwikkeling van pseudohifes word gekorreleer
met ander fisiologiese prosesse, soos styselafbraak en die penetrerende groei van
selle op agar-bevattende media. Mss11p vervul 'n sentrale rol in die regulering van
gene wat vir hierdie prosesse benodig word en reguleer die uitdrukking van FL011,
wat kodeer vir 'n selwandproteïen wat krities is vir die ontwikkeling van pseudohifes,
en STA2, wat kodeer vir 'n ekstrasellulêre glukoamilase wat vir die afbraak van stysel
benodig word.
Die doel van hierdie studie was om Mss11p-funksie te karakteriseer. Deur middel
van oorproduksie is Mss11p as die induseerder van penetrerende groei,
selverlenging en flokkulasie geïdentifiseer. Verder is bevind dat MSS11-delesie lei tot
verhoogde biomassa formasie, en dat dieselfde delesie lei tot 'n oorkoming van 'n
groeidefek van gis van die 2:1278b genetiese agtergrond wat met die RAS2val19aleel
op nie-fermenteerbare koolstofbronne getransformeer is. Biochemiese analise dui
daarop dat Mss11p 'n nukluêre proteïen is van ongeveer 97 kDa in oënskynlike
grootte, wat teen lae vlakke in gis onderhou word. Die data stel 'n model voor waarin
Mss11p as bemiddelaar optree vir die transkripsionele regulering van verskeie gene.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53433 |
| Date | 03 1900 |
| Creators | Bester, Michael C. (Michael Christiaan) |
| Contributors | Pretorius, I. S., Bauer, F. F., Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 82 p. : ill. (some col.) |
| Rights | Stellenbosch University |
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