Strikingly, respiration-deficient mutants are competent for this starvation-induced mitophagy, suggesting that oxidative stress is not a general prerequisite for degradation of mitochondria.
For example, some mutants are competent for recruitment to depolarized mitochondria, but are unable to stimulate the degradation of damaged mitochondria (19– 23).
These results were surprising as extensive evidence has shown that constitutively trimerized mammalian HSF1 mutants are competent to bind DNA in vitro using gel shift analysis (Rabindran et al. 1993; Zuo et al. 1994, 1995; Farkas et al. 1998).
The ubiquitin chains conjugated to Tax appeared to be predominantly K63-linked, since a ubiquitin mutant lacking K63 (K63R) was defective in mediating Tax ubiquitination, whereas the K48R ubiquitin mutant was competent in mediating Tax ubiquitination.
Importantly, the double mutant D140A/D144A ablated Notch-dependent activation to a level similar to that observed for F207A, even though this mutant is competent for Notch-1 binding in vitro.
An ELISA-based Notch-binding assay first demonstrated that this double mutant was competent for Notch-1 binding, in contrast to a previously identified ablative DSL domain mutant (F207A) control.
Likewise, mutation of the GAG-binding sites in CCL5, CCL7 and CXCL12 yielded chemokine mutants that were competent in receptor activation in vitro but possessed anti-inflammatory dominant-negative properties in animal models of inflammation, including atherosclerosis (Ali et al, 2010; Braunersreuther et al, 2008; O'Boyle et al, 2009).
A second round of infection of target Jurkat and U937 cells with supernatants collected 18 days after the first infection allowed us to conclude that all mutant viruses were competent in terms of infectivity in both cell lines (data not shown).
All those mutants were biologically competent in several cell culture assays, maintaining typical FGF-1 activities, such as binding to specific cell surface receptors and activation of downstream signaling pathways.
However, compared to the wild-type proteins, these mutants were equally competent in the activation of Grp78 and Grp94 promoters.
