Dear Editor, The COVID-19 pandemic worldwide is caused by a novel coronavirus SARS-CoV-2 (the severe acute respiratory syndrome coronavirus 2). 1 After viral invasion into the host cells, the~30 kb viral genome RNA injected is translated into structural and nonstructural proteins to replicate viral genome and assemble more viral particles. Many copies of nucleocapsid (N) protein can bind to viral genome RNA and pack it into~100 nm particles, assisting membrane (M) and envelope (E) proteins to efficiently assemble the viral envelope. 2 The exact molecular mechanism by which N protein packs up the viral genome still remains elusive. An N protein of SARS-CoV-2 consists of an N-terminal RNAbinding domain (NTD) and a C-terminal dimerization domain (CTD) and shares~90% sequence identity with N protein of SARS-CoV (Supplementary information, Fig. S1a). The regions located between the N-terminus and NTD, between NTD and CTD, and between CTD and the C-terminus of the N protein of SARS-CoV-2 (thereafter referred to as N protein) are predicted to be intrinsically disordered (Supplementary information, Fig. S1b, c). At neutral pH, the N protein is positively charged (+24 e), consistent with its strong binding affinity with negatively charged

Edited by Lev KisselevAbstract The small molecule coralyne was found to bind preferentially and strongly to single-stranded poly(A) with an apparent association constant (K a ) of (1.8 ± 0.3) · 10 6 M À1 . Binding of coralyne to poly(A) is predominantly enthalpically driven with a stoichiometry of one coralyne per four adenine bases. Poly(A) forms a coralyne dependent secondary structure with a melting temperature of 60°C, for the conditions of our study.

An enzyme responsive nanoparticle system that uses a DNA-gold nanoparticle (AuNP) assembly as the substrate has been developed for the simple, sensitive, and universal monitoring of restriction endonucleases in real time. This new assay takes advantage of the palindromic recognition sequence of the restriction nucleases and the unique optical properties of AuNPs and is simpler than the procedure previously described by by Xu et al. (Angew. Chem. Int. Ed. Engl. 2007, 46, 3468-3470). Because it involves only one type of ssDNA modified AuNPs, this assay can be directed toward most of the endonucleases by simply changing the recognition sequence found within the linker DNA. In addition, the endonuclease activity could be quantitatively analyzed by the value of the reciprocal of hydrolysis half time (t(1/2)(-1)). Furthermore, our new design could also be applied to the assay of methyltransferase activity since the methylation of DNA inhibits its cleavage by the corresponding restriction endonuclease, and thus, this new methodology can be easily adapted to high-throughput screening of methyltransferase inhibitors.