SummaryThe bacterial tRNA Lys -specific anticodon nuclease is known as a phage T4 exclusion system. In the uninfected host cell anticodon nuclease is kept latent due to the association of its core protein PrrC with the DNA restriction-modification endonuclease EcoprrI. Stp, the T4-encoded peptide inhibitor of EcoprrI activates the latent enzyme. Previous in vitro work indicated that the activation by Stp is sensitive to DNase and requires added nucleotides. Biochemical and mutational data reported here suggest that Stp activates the latent holoenzyme when its EcoprrI component is tethered to a cognate DNA substrate. Moreover, the activation is driven by GTP hydrolysis, possibly mediated by the NTPase domain of PrrC. The data also reveal that Stp can be replaced as the activator of latent anticodon nuclease by certain pyrimidine nucleotides, the most potent of which is dTTP. The activation by dTTP likewise requires an EcoprrI DNA substrate and GTP hydrolysis but involves a different form of the latent holoenzyme/DNA complex. Moreover, whereas Stp relays its activating effect through EcoprrI, dTTP targets PrrC. The activation of the latent enzyme by a normal cell constituent hints that anticodon nuclease plays additional roles, other than warding off phage T4 infection.
Recent data suggest that the digital divide between White and minority youth persists, particularly in terms of home access to computers and the Internet. Community technology centers (CTCs) are an important alterative access point, especially for low-income youth of color. Such institutions, however, do much more, providing not just access, but general youth development, including the opportunity for youth to voice their stories, contribute to community-building, and expand networks. The authors use qualitative data collected at five CTCs nationwide to examine the ways that youth engage in CTCs and link these activities to a youth development framework.The authors draw lessons for future CTC practice, highlighting the importance of both bonding and bridging social capital in thinking through future programming.
Aluminum alloy panels joined with stainless steel fasteners have been known to occur in aerospace structures, due to their respective optimized mechanical properties. When connected via a conductive solution, a high-driving force for galvanic corrosion is present. The combination of the dissimilar materials, indicating galvanic corrosion, and complex geometry of the occluded fastener hole, indicating crevice corrosion, leads to the detrimental combined effect of galvanic-induced crevice corrosion, as investigated previously in Part I. The present work extends the validated finite element method (FEM) model to predict the current distribution and magnitude in a variety of geometric and environmental conditions, with the goal of preventing corrosion damage within the highly-susceptible fastener hole. Specifically, water layer thicknesses ranging from bulk full-immersion (800 μm) to atmospheric (89 μm) conditions was investigated, as well as the impact of external scribe dimensions. Two avenues for mitigation were determined, 1) to force the majority of current away from the fastener hole and onto the bulk surface of the panel, and 2) to lower the overall galvanic coupling current. A random forest machine learning algorithm was developed to generalize the FEM predictions and create an open-source applicable prediction tool.
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