Yeast Mating Type Switching

[niravana21]

In yeast, mating type switching is restricted to mother cells. The presence of the Ash1p protein is thought to control the activity of the HO gene in daughter cells:

PART A
How is this cell asymmetry brought about during the yeast cell cycle? What would be the effect of (i) of introducing a mutation into the ASH1 gene, and (ii) deleting the UTR region of the ASH1 mRNA?
diagram: http://i214.photobucket.com/albums/cc35 ... /partA.png

PART B:
(b) A similar kind of cell asymmetry seems to occur during cell division in the bacterium, Caulobacter crescentus, in which a sessile (stalked) mother cell and a motile (flagellated) daughter cell are generated at the end of the cell cycle:
diagram: http://i214.photobucket.com/albums/cc35 ... /partB.png

any type of help will be greatly appreciated.

[JackBean]

what is your question in B?

A: Obviously it's the ASH1 mRNA location, which leads to the asymmetry. This assymetry is accomplished with the sequence at 3'-UTR, thus if you deleted it, the cell won't be polarized anymore and both new cells will become mother cells. On the other hand, if you mutated ASH1, so that it won't function, you would get daugther cell from your mother cell.

[niravana21]

thanks!
B) How does the establishment of cell asymmetry in Caulobacter compare and contrast with the yeast model? Provide an illustrated response.

[fiona1985]

Cell divisions that produce progeny differing in their patterns of gene expression are key to the development of multicellular organisms. In the budding yeast Saccharomyces cerevisiae, mother cells but not daughter cells can switch mating type because they selectively express the HO endonuclease gene. This asymmetry is due to the preferential accumulation of an unstable transcriptional repressor protein, Ash1p, in daughter cell nuclei. Here it is shown thatASH1 messenger RNA (mRNA) preferentially accumulates in daughter cells by a process that is dependent on actin and myosin. A cis-acting element in the 3′-untranslated region of ASH1mRNA is sufficient to localize a chimeric RNA to daughter cells. These results suggest that localization of mRNA may have been an early property of the eukaryotic lineage.