Interaction of the human immunodeficiency virus type 1 (HIV-1) Rev protein with a structured region within env mRNA (termed RRE) mediates the export of virus structural mRNAs from the nucleus to the cytoplasm. We show that the region encompassing the basic stretch of amino acids is essential for the ability of Rev to bind to RRE RNA and function in vivo. By use of a functional truncated Rev protein in conjunction with authentic Rev, effects on gel mobilities of the Rev-RRE RNA complex attributable to multimerization of Rev protein were observed. Rev proteins, unable to multimerize, failed to bind RRE RNA. Identification of Rev mutants capable of forming multimers, but unable to bind RRE RNA, suggests that the multimerization and RNAbinding domains can be distinguished and that multimerization is likely a prerequisite for formation of the RRE RNA-binding site. A mutant Rev protein, shown previously to function as a trans-dominant inhibitor of Rev function, bound to RRE RNA as a multimer to a similar extent as wild-type Rev. This observation is consistent with the hypothesis that regulation of HIV gene expression by Rev involves the interaction with cellular factors and that the trans-dominant Rev is probably defective in this function.

Sik (mouse Src-related intestinal kinase) and its orthologue BRK (human breast tumor kinase) are intracellular tyrosine kinases that are distantly related to the Src family and have a similar structure, but they lack the myristoylation signal. Here we demonstrate that Sik and BRK associate with the RNA binding protein Sam68 (Src associated during mitosis, 68 kDa). We found that Sik interacts with Sam68 through its SH3 and SH2 domains and that the proline-rich P3 region of Sam68 is required for Sik and BRK SH3 binding. In the transformed HT29 adenocarcinoma cell cell line, endogenous BRK and Sam68 colocalize in Sam68-SLM nuclear bodies (SNBs), while transfected Sik and Sam68 are localized diffusely in the nucleoplasm of nontransformed NMuMG mammary epithelial cells. Transfected Sik phosphorylates Sam68 in SNBs in HT29 cells and in the nucleoplasm of NMuMG cells. In functional studies, expression of Sik abolished the ability of Sam68 to bind RNA and act as a cellular Rev homologue. While Sam68 is a substrate for Src family kinases during mitosis, Sik/BRK is the first identified tyrosine kinase that can phosphorylate Sam68 and regulate its activity within the nucleus, where it resides during most of the cell cycle.

The development of new methods for direct viral detection using streamlined and ideally reagent-free assays is a timely and important, but challenging, problem. The challenge of combatting the COVID-19 pandemic has been exacerbated by the lack of rapid and effective methods to identify viral pathogens like SARS-CoV-2 on-demand. Existing gold standard nucleic acid-based approaches require enzymatic amplification to achieve clinically relevant levels of sensitivity and are not typically used outside of a laboratory setting. Here, we report reagent-free viral sensing that directly reads out the presence of viral particles in 5 minutes using only a sensor-modified electrode chip. The approach relies on a class of electrode-tethered sensors bearing an analyte-binding antibody displayed on a negatively charged DNA linker that also features a tethered redox probe. When a positive potential is applied, the sensor is transported to the electrode surface. Using chronoamperometry, the presence of viral particles and proteins can be detected as these species increase the hydrodynamic drag on the sensor. This report is the first virus-detecting assay that uses the kinetic response of a probe/virus complex to analyze the complexation state of the antibody. We demonstrate the performance of this sensing approach as a means to detect, within 5 min, the presence of the SARS-CoV-2 virus and its associated spike protein in test samples and in unprocessed patient saliva.

Host recognition of pathogen-associated molecular patterns (PAMPs) initiates an innate immune response that is critical for pathogen elimination and engagement of adaptive immunity. Here we show that mammalian cells can detect and respond to the bacterial-derived monosaccharide heptose-1,7-bisphosphate (HBP). A metabolic intermediate in lipopolysaccharide biosynthesis, HBP is highly conserved in Gram-negative bacteria, yet absent from eukaryotic cells. Detection of HBP within the host cytosol activated the nuclear facto κB pathway in vitro and induced innate and adaptive immune responses in vivo. Moreover, we used a genome-wide RNA interference screen to uncover an innate immune signaling axis, mediated by phosphorylation-dependent oligomerization of the TRAF-interacting protein with forkhead-associated domain (TIFA) that is triggered by HBP. Thus, HBP is a PAMP that activates TIFA-dependent immunity to Gram-negative bacteria.

A region in the human immunodeficiency virus (HIV) env message, with the potential to form a complex secondary structure (designated RRE), interacts with the rev protein (Rev). This interaction is believed to mediate export of HIV structural messenger RNAs from the nucleus to the cytoplasm. In this report the regions essential for Rev interaction with the RRE are further characterized and the functional significance of Rev-RRE interaction in vivo is examined. A single hairpin loop structure within the RRE was found to be a primary determinant for Rev binding in vitro and Rev response in vivo. Maintenance of secondary structure, rather than primary nucleotide sequence alone, appeared to be necessary for Rev-RNA interaction, which distinguishes it from the mechanism for cis-acting elements in DNA. Limited changes within the 200 nucleotides, which preserved the proper RRE conformational structure, were well tolerated for Rev binding and function. Thus, variation among the RRE elements present in the diverse HIV isolates would have little, if any, effect on Rev responsiveness.