In this issue

MALDI‐TOF “Flip‐flop” drug susceptibility test pp. 4627–4631 The emergence of drug‐resistant pathogens over the last 50 years has presented/created major problems for clinical microbiologists: is the bug resistant to a given drug and, if so, how resistant? Current susceptibility tests are not as clear cut as might be wished, requiring an educated eyeball for the final determination. Marinach et al . have taken a new approach to this problem, applying the power of a MALDI‐TOF mass spectrometer to “fingerprint” organisms and extracts rapidly and inexpensively. Using an acid extract of Candida albicans , which had been exposed to various concentrations of Fluconazole, they found the MALDI‐TOF mass spectrum showed an “on–off” response: in one example there were no peak differences between low control and up to 2 μg/mL, then, clear changes were visible from 4 μg/mL and up.Proteome in motion pp. 4674–4685 Pulse‐chase has been one of the most powerful techniques in molecular biology for eliciting relationships and pathways. Here it is applied to the yeast proteome to ask the “Big Bang” question: what is the proteome at the instant of synthesis and what does it become in time? Massoni et al . used [ 35 S]‐methionine to pulse label Saccharomyces cerevisiae , sampling after various times, from 0.1 to 4 doublings. Analyzing by 2‐D electrophoresis, these researchers were able to detect more than 500 spots and determine protein half‐lives down to ∼15 min. Spots that appeared or disappeared during the chase period were undergoing post‐translational modification (PTM). The most common PTM is seen as a p I shift due to phosphorylation. A number of unusual PTMs were confirmed. Rates of PTM appearance ranged from virtually immediately upon expression to several hours.Quick switch key for mitochondria pp. 4787–4798 One of the benefits of working with Saccharomyces cerevisiae is the speed at which it can switch between aerobic and anaerobic growth. How do the mitochondria do that? The answer: they don't do a total shut‐down when subjected to anaerobic conditions. They retain the energetically expensive mitochondrial ribosomes and most of the multi‐subunit respiratory complex components. To gather this kind of information, Helbig et al . required better starting material than had been used in previously published studies, they required separately grown and labeled aerobic and anaerobic cell lysates. The final experimental design was in three parts and produced quantitative results for mitochondrial components under virtually identical conditions for aerobic and anaerobic growth. Blue native (BN)‐PAGE was used for improved coverage of membrane proteins.