Protein phosphatase 2A (PP2A) is an important regulator of signal transduction pathways and a tumor suppressor. Phosphorylation of the PP2A catalytic subunit (PP2AC) at tyrosine 307 has been claimed to inactivate PP2A and was examined in more than 180 studies using commercial antibodies, but this modification was never identified using mass spectrometry. Here we show that the most cited pTyr307 monoclonal antibodies, E155 and F-8, are not specific for phosphorylated Tyr307 but instead are hampered by PP2AC methylation at leucine 309 or phosphorylation at threonine 304. Other pTyr307 antibodies are sensitive to PP2AC methylation as well, and some cross-react with pTyr residues in general, including phosphorylated hemagglutinin tags. We identify pTyr307 using targeted mass spectrometry after transient overexpression of PP2AC and Src kinase. Yet under such conditions, none of the tested antibodies show exclusive pTyr307 specificity. Thus, data generated using these antibodies need to be revisited, and the mechanism of PP2A inactivation needs to be redefined. Aberrant hyperphosphorylation of the protein phosphatase 2A catalytic subunit (PP2Ac) at Tyr307 has been associated with aggressive disease and poor clinical outcome in multiple cancers. However, the study of reversible phosphorylation at this site has relied entirely upon the use of antibodies-most prominently, the clone E155. Here, we provide evidence that the E155 and F-8 phospho-Tyr307 antibodies cannot differentiate between phosphorylated and unphosphorylated forms of PP2Ac. The form of PP2Ac bound by these antibodies in H358 cells is unphosphorylated at the C-terminal tail. Furthermore, these antibodies are sensitive to additional protein modifications that occur near Tyr307, including Thr304 phosphorylation and Leu309 methylation, when these post-translational modifications are present. Thus, studies that used these antibodies to report PP2Ac hyperphosphorylation require reinterpretation, as these antibodies cannot be reliably used as readouts for a single PP2Ac post-translational modification (PTM) change. Cardiac ischemia leads to the loss of myocardial tissue and the activation of a repair process that culminates in the formation of a scar whose structural characteristics dictate propensity to favorable healing or detrimental cardiac wall rupture. To elucidate the cellular processes underlying scar formation, here we perform unbiased single-cell mRNA sequencing of interstitial cells isolated from infarcted mouse hearts carrying a genetic tracer that labels epicardial-derived cells. Sixteen interstitial cell clusters are revealed, five of which were of epicardial origin. Focusing on stromal cells, we define 11 sub-clusters, including diverse cell states of epicardial- and endocardial-derived fibroblasts. Comparing transcript profiles from post-infarction hearts in C57BL/6J and 129S1/SvImJ inbred mice, which displays a marked divergence in the frequency of cardiac rupture, uncovers an early increase in activated myofibroblasts, enhanced collagen deposition, and persistent acute phase response in 129S1/SvImJ mouse hearts, defining a crucial time window of pathological remodeling that predicts disease outcome. As pH is fundamental to all biological processes, pH-responsive bacterial genetic circuits enable precise sensing in any environment. Where the unintentional release of engineered bacteria poses a concern, coupling pH sensing to the expression of a toxin creates an effective bacterial containment system. Here, we present a pH-sensitive kill switch (acidic termination of replicating population [acidTRP]), based on the Escherichia coli asr promoter, with a survival ratio of less then 1 in 106. We integrate acidTRP with cryodeath to produce a 2-factor containment system with a combined survival ratio of less then 1 in 1011 while maintaining evolutionary stability. We further develop a pulse-counting circuit with single-cell readout for each administered stimulus pulse. Sodium butyrate mw We use this pulse counter to record multiple pH changes and combine it with acidTRP to make a 2-count acid-sensitive kill switch. These results demonstrate the ability to build complex genetic systems for biological containment. Bacterial small RNAs (sRNAs) are posttranscriptional regulators of gene expression that base pair with complementary sequences on target mRNAs, often in association with the chaperone Hfq. Here, using experimentally identified sRNA-target pairs, along with gene expression measurements, we assess basic principles of regulation by sRNAs. We show that the sRNA sequence dictates the target repertoire, as point mutations in the sRNA shift the target set correspondingly. We distinguish two subsets of targets targets showing changes in expression levels under overexpression of their sRNA regulator and unaffected targets that interact more sporadically with the sRNA. These differences among targets are associated with their Hfq occupancy, rather than with the sRNA-target base-pairing potential. Our results suggest that competition among targets over Hfq binding plays a major role in the regulatory outcome, possibly awarding targets with higher Hfq binding efficiency an advantage in the competition over binding to the sRNA. Timely completion of DNA replication is central to accurate cell division and to the maintenance of genomic stability. However, certain DNA-protein interactions can physically impede DNA replication fork progression. Cells remove or bypass these physical impediments by different mechanisms to preserve DNA macromolecule integrity and genome stability. In Saccharomyces cerevisiae, Wss1, the DNA-protein crosslink repair protease, allows cells to tolerate hydroxyurea-induced replication stress, but the underlying mechanism by which Wss1 promotes this function has remained unknown. Here, we report that Wss1 provides cells tolerance to replication stress by directly degrading core histone subunits that non-specifically and non-covalently bind to single-stranded DNA. Unlike Wss1-dependent proteolysis of covalent DNA-protein crosslinks, proteolysis of histones does not require Cdc48 nor SUMO-binding activities. Wss1 thus acts as a multi-functional protease capable of targeting a broad range of covalent and non-covalent DNA-binding proteins to preserve genome stability during adverse conditions.