In addition to the high-frequency, low-impact disturbances, the forests are also subject to low-frequency catastrophes, such as hurricanes in the region investigated here.
This allows us to predict how the evolutionary stable level of persisters depends upon population demographic parameters such as intensity of resource competition, the frequency of catastrophes such as antibiotic treatment, and the genetic structure (heterogeneity) of populations.
Early studies showed that depletion of kinesin-13 XKCM1 did not affect the rate of microtubule growth or shrinkage in extracts, but did result in a 4-fold decrease in the frequency of catastrophes (Walczak et al., 1996).
Conversely, overexpression of kinesin-13 in tissue culture cells leads to an increase in the frequency of catastrophes (Kline-Smith and Walczak, 2002) and a reduction in the number of microtubules (Maney et al, 1998), again consistent with kinesin-13 proteins being depolymerases in vivo.
Catastrophe events, on the other hand, display low sensitivity with respect to tubulin concentration, such that an increase in tubulin concentration leads to a moderate suppression of microtubule catastrophe at the plus end 2, 3: "the frequency of catastrophe is not steeply dependent on elongation rate" 2. Furthermore, microtubule catastrophe cannot be described as a single-step random process.
Although the harvest occurred only every 86 years on average, this was equivalent to a low frequency natural catastrophe reducing substantially the fraction of the landscape in old-growth state.
This resulted in a decrease in the frequency of catastrophe for mal3Δ mtr1Δ cells.
mtr1p appears to increase the frequency of catastrophe, a role antagonistic to mal3p.
However, mtr1p appears to help increase microtubule growth velocity and to increase the frequency of catastrophe.
The β T238A mutation stimulated spontaneous nucleation and reduced the frequency of catastrophe and the rate of shrinking, all without substantially affecting elongation.
Further, the role of mtr1p in increasing the frequency of catastrophe is consistent with its role in decreasing the microtubule dwell-time.
