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Improving Constraints on Planetary Interiors With PPs Receiver Functions

ABSTRACT: Abstract Seismological constraints obtained from receiver function (RF) analysis provide important information about the crust and mantle structure. Here, we explore the utility of the free‐surface multiple of the P‐wave (PP) and the corresponding conversions in RF analysis. Using earthquake records, we demonstrate the efficacy of PPs‐RFs before illustrating how they become especially useful when limited data is available in typical planetary missions. Using a transdimensional hierarchical Bayesian deconvolution approach, we compute robust P‐to‐S (Ps)‐ and PPs‐RFs with InSight recordings of five marsquakes. Our Ps‐RF results verify the direct Ps converted phases reported by previous RF analyses with increased coherence and reveal other phases including the primary multiple reverberating within the uppermost layer of the Martian crust. Unlike the Ps‐RFs, our PPs‐RFs lack an arrival at 7.2 s lag time. Whereas Ps‐RFs on Mars could be equally well fit by a two‐ or three‐layer crust, synthetic modeling shows that the disappearance of the 7.2 s phase requires a three‐layer crust, and is highly sensitive to velocity and thickness of intra‐crustal layers. We show that a three‐layer crust is also preferred by S‐to‐P (Sp)‐RFs. While the deepest interface of the three‐layer crust represents the crust‐mantle interface beneath the InSight landing site, the other two interfaces at shallower depths could represent a sharp transition between either fractured and unfractured materials or thick basaltic flows and pre‐existing crustal materials. PPs‐RFs can provide complementary constraints and maximize the extraction of information about crustal structure in data‐constrained circumstances such as planetary missions. Key Points We compute robust P‐to‐S (Ps)‐, P‐waves (PPs)‐, and S‐to‐P (Sp)‐receiver functions (RFs) to infer properties of the crustal layers beneath the InSight lander in Elysium Planitia Sp‐RFs as well as observed variability of the 7.2 s phase between Ps‐ and PPs‐RFs require a three‐layer crust PPs‐RFs can provide complementary constraints for crustal imaging on Earth and other planetary bodies

SUBMITTER: Kim D

PROVIDER: S-EPMC8597591 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundThe Escherichia coli response regulator NarL controls transcription of genes involved in nitrate respiration during anaerobiosis. NarL consists of two domains joined by a linker that wraps around the interdomain interface. Phosphorylation of the NarL N-terminal receiver domain (RD) releases the, otherwise sequestered, C-terminal output domain (OD) that subsequently binds specific DNA promoter sites to repress or activate gene expression. The aim of this study is to investigate the extent to which the NarL OD and RD function independently to regulate transcription, and the affect of the linker on OD function.ResultsNarL OD constructs containing different linker segments were examined for their ability to repress frdA-lacZ or activate narG-lacZ reporter fusion genes. These in vivo expression assays revealed that the NarL OD, in the absence or presence of linker helix α6, constitutively repressed frdA-lacZ expression regardless of nitrate availability. However, the presence of the linker loop α5-α6 reversed this repression and also showed impaired DNA binding in vitro. The OD alone could not activate narG-lacZ expression; this activity required the presence of the NarL RD. A footprint assay demonstrated that the NarL OD only partially bound recognition sites at the narG promoter, and the binding affinity was increased by the presence of the phosphorylated RD. Analytical ultracentrifugation used to examine domain oligomerization showed that the NarL RD forms dimers in solution while the OD is monomeric.ConclusionsThe NarL RD operates as an on-off switch to occlude or release the OD in a nitrate-responsive manner, but has additional roles to directly stimulate transcription at promoters for which the OD lacks independent function. One such role of the RD is to enhance the DNA binding affinity of the OD to target promoter sites. The data also imply that NarL phosphorylation results in RD dimerization and in the separation of the entire linker region from the OD.

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Improving Constraints on Planetary Interiors With PPs Receiver Functions

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