> From: "Dr M.J. Pocklington" <poc at leicester.ac.uk>
> Subject: RE: Germination
> Date: 8 Jul 1994 19:31:13 +0100
> The yeast strains I work with (S288C derivatives) germinate "perfectly"
> happily in the absence of added glucose (ie on glycerol YP, galactose YP or
> even YP only plates).
this is entirely different from "the absence of glucose", and I wonder
what your definition of "perfectly" might be? ;-)
...This does not really surprise me, since it would be a
> silly yeast beast that missed out on the opportunity to grow on a medium that
> it could normally grow on.
But S288C derivs do NOT normally grow on YP only!
...What does surprise me is the apparent obsession,
> without good reason, with a glucose receptor.
obsessions, by definition, have no good reason, and it is not possible
to "understand" them. When you can prove that no glucose receptor
exists, you'll have some suggestive negative results. Maybe one of
those obsessed people whom you can't understand will eventually come
up with a glucose receptor gene. Now, THAT would be amazing!
>> I suspect that the early work identifying glucose as necessary for
> germination, really only showed that a metabolisable carbon source
> was necessary for germination. Of course I may be wrong: glucose is a pretty
> central point in metabolism, and I suppose that by monitoring (internal, of
> course) glucose levels, the cellular growth system could then mount an
> appropriate response. But surely it would make a whole lot more sense if the
> germination response was signalled by cyclic nucleotide or NTP or NTP/NDP
> levels, or even a H+ or pH gradient. Then there would be no need for a
> multiplicity of "receptors"; and such a nutritional status indicator would
> be closer to what really matters in the cell (energy availability in general);
> and it is evolutionarily more sensible. And after all, it seems like thats
> how the starvation response is initiated in the first place. Perhaps thats
> where the hetrotrimeric G-proteins and ras come in (sensing GTP/GDP levels,
> consequent upon ATP levels, ultimately).
This is just a little arrogant, I think (yeah, I know, it takes one
to know one ;-) Since we don't know what a spore "really" is, nor why,
in evolution, such structures persist, it seems premature to think that
indicators of nutritional status relevant to yeast would even be known to
us humans, in the first place, and that they would be relevant to germination
signalling in the second place. This needs more data and less speculation.
>> Evolution in a world of sugar may have selected for yeast that do indeed have
> a glucose receptor. Fine -lets find it. But by the above reasoning, not only
> is such a receptor unneccessary, but if there was one, it would likely be an
> evolutionary speciality -a side issue.
Well, but aren't evolutionary specialties sort of the core of biology?
>> Sensing a return to a happy nutritional status isn't the end of the story as
> far as germination is concerned. All that heat, chemical, dryness, UV, etc.
> -resistant packaging has to be undone before the cell cycle can get going
> again, and it shouldn't surprise me if there was an extensive machinery for
> (un)doing it. I bet a mutational approach would discover the genes for
> this/these function(s) rather than those involved in sensing nutritional
Well, I'm not sure yeast spores are any more resistant than stationary
phase vegetative cells (as Lenore Neigeborn also noted, these guys are not
like bacterial endospores of the Bacillus/Clostridium type), but I think
you're right about a multi-step process being required for total germination,
and you're absolutely right about genetics as the proper tool to analyze it.
I would guess, though, that ger mutants might well reveal sensory proteins
at the front-end of the process.
>>> Michael Pocklington
rapr at med.pitt.edu
disclaimer: I have no financial interest in any of this: I don't even work
on yeast any more, except as a host for YACs and occasional YUKs.