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We present a detailed study on the spatially resolved polycyclic aromatic hydrocarbon (PAH) emission properties in the (circum)nuclear region (NR) and extranuclear regions (ENRs) of M51a using Spitzer -IRS (infrared spectrograph) observations. Correlations among PAH intensity ratios are examined with respect to each other, local physical parameters, galactocentric distance (R g), and very small grain (VSG) emission. Additional comparison is performed with the mid-infrared emission features in the H  ii regions of M33 and M83. The NR exhibits the strongest correlation among the PAH intensity ratios, whereas ENRs are showing increased scatter attributed to interstellar medium emission. Overall, the radiation field hardness has a higher impact on PAH emission than metallicity, with the latter regulating PAH variance as a function of R g. Specifically, the variance of PAH emission with respect to the different physical parameters suggests a higher rate of small/medium PAH processing compared to large PAHs and a higher ratio of small-to-large PAHs formed with increasing galactocentric distance. We find similarities between the 7.7 |$\mu$| m carriers in M51a's NR and M83's H  ii regions, the 8.6 |$\mu$| m carriers in M51a's NR and M33 H  ii regions, and both types of carriers between M51a's ENRs, M33's, and M83's H  ii regions. We have identified a positive correlation between PAH/VSG and the PAH intensity ratios. We conclude that the relative abundance of PAHs and VSG is not solely driven by the hardness of the radiation field. [ABSTRACT FROM AUTHOR]

Phosphofurin acidic cluster sorting protein 1 (PACS‐1) is canonically a cytosolic trafficking protein, yet recent reports have described nuclear roles for PACS‐1. Herein, we sought to define the nuclear transport mechanism of PACS‐1. We demonstrate that PACS‐1 nucleocytoplasmic trafficking is dependent on its interaction with the nuclear transport receptors importin alpha 5 and exportin 1. PACS‐1 nuclear entry and exit are defined by a nuclear localization signal (NLS, residues 311‐318) and nuclear export signal (NES3, residues 366‐375). Mutation of the PACS‐1 NLS and NES3 altered the localization of a complex formed between PACS‐1 and an RNA‐binding protein, polypyrimidine tract‐binding protein 1. Overall, we identify the nuclear localization mechanism of PACS‐1 and highlight a potential role for PACS‐1 in RNA‐binding protein trafficking. [ABSTRACT FROM AUTHOR]