Effect of Hsp26 on Yeast Growth

K. Unno, T. Kishido, and S. Okada, “Effect of over-expressed Hsp26 on cell growth in yeast,” Biol. Pharm Bull., vol. 21, pp. 631–633, 1998.

In an attempt to further understand the poorly written paper I summarized yesterday I’m going back to read the paper they cited pretty frequently. Hopefully this paper will answer some of the questions I had yesterday. Note time:

  • The motivation for this study is that there has been no observation of the effects of the over-expression or depression of hsp26. Apparently hsp26 is induced during the transition of log-phase growth to stationary phase in yeast growth.
  • As they mentioned in yesterday’s paper (this one is earlier by a few years), the yeast cells used were ssa1ssa2 and have a slower growth rate than the wt.
  • Like the methods from yesterday, they picked clones of ssa1ssa2. However, this time the clones they chose had different doubling times from each other. Yesterday they chose clones whose doubling times were comparable to the wt.
  • cells were incubated at 25C in a minimal dextrose medium (YPd? hahaha) supplemented with nutrients but lacking uracil. WHY???
  • They plot the doubling time of the clones of ssa1ssa2 and the wt. It didn’t occur to me that the growth rate of clones could be different. This may be interesting to explore for my D2O variant strain. It should be noted that the doubling time of the wt strain had little variance amongst clones. What is the mechanism for this?
  • Exactly what is the difference between clones of the wt and clones of ssa1ssa2???
  • they then relate the expression of hsp26 to doubling time and compare that to other proteins (hsp70, hsp90, hsp104, Ssb, and Kar2). They find that hsp26 is more closely correlated to doubling time than the other 3 hsp’s and make no claim about Ssb and Kar2. But they do state that the amounts of Ssb and Kar2 in the clones is similar to the wt. This is sort of true.

So based on subtle information in this paper, it seems the mutant ssa1ssa2 lacks the genes Ssa1 and Ssa2 which make the hsp70 enzyme. But this paper mentions that Ssa4 is inducible and also produces hsp70 when induced. So in yesterday’s paper when they said there was no hsp70 but then they got hsp70, I’m guessing they induced the Ssa4 gene to get some hsp70. Good thing they mentioned that!

In this paper the induced hsp70 levels are less than the wt, and their data shows that hsp70 levels increase with increased doubling time. So yeast that lack Ssa1 and Ssa2 but have Ssa4 have higher levels of hsp26 (than wt) and almost normal levels of hsp70 are at risk for longer growth rates (doubling time). So the proteins may be linked in the extreme case that the Ssa1 and 2 genes are off and the Ssa4 gene is on (both produce hsp70).

But how does this information relate to the paper yesterday? It doesn’t really, but it may explain why they were seemingly contradicting the amount of hsp70 they had in their cells.

Ok just quickly rereading the first few pages of yesterday’s paper and I still have no idea what is going on. No matter. Their results claim to show that some clone of ssa1ssa2, which is beyond arbitrary, is D2O tolerant. I’m not too sure that their methods apply to what I’m doing, since they are just looking for deuterium resistance and not necessarily an organism that is made of D instead of H. I will go over yesterday’s paper again later tonight/early tomorrow to make sure things still make no sense (but maybe I’ll have a moment of clarity?).