My name is Michael Stark, and in my presentation I'm going to tell you
about chromosome bi-orientation in the budding yeast Saccharomyces cerevisiae.
There are three main topics that I'd like to cover in my presentation.
The first one is what chromosome bi-orientation is, and why it's important.
Then I would like to go on to discuss the mechanisms that
ensure that chromosome bi-orientation occurs.
Finally, I will move on to consider how the mechanisms that ensure chromosome
bi-orientation are themselves regulated.
We'll be focusing principally on work from the budding yeast
Saccharomyces cerevisiae, as the model system in which many of these
mechanisms have been established.
Firstly, what is chromosome bi-orientation and why is it important?
Early in the cell division cycle,
each chromosome is present as a single unreplicated copy.
In yeast, for most of the cell division cycle,
chromosomes are attached to microtubules.
The point of attachment to the microtubule is termed the 'kinetochore',
this is a protein complex that is assembled on the centromeric region of each chromosome.
The microtubules are nucleated from the spindle pole bodies.
During the replicative phase each chromosome is duplicated,
but the two copies (which are termed 'sister chromatids') remain firmly associated,
held together by protein complexes called cohesin.
After replication, the critical thing for ensuring faithful segregation of
each chromosome is that the two sister chromatids
must become attached to microtubules from opposite spindle poles.
This is what we term 'chromosome bi-orientation'.