The HIV-1 Pr55^Gag precursor specifically selects genomic RNA (gRNA) from a large variety of cellular and spliced viral RNAs (svRNAs), however the molecular mechanisms of this selective recognition remains poorly understood. To gain better understanding of this process, we analyzed the interactions between Pr55^Gag and a large panel of viral RNA (vRNA) fragments encompassing the main packaging signal (Psi) and its flanking regions by fluorescence spectroscopy. We showed that the gRNA harbors a high affinity binding site which is absent from svRNA species, suggesting that this site might be crucial for selecting the HIV-1 genome. Our stoichiometry analysis of protein/RNA complexes revealed that few copies of Pr55^Gag specifically associate with the 5′ region of the gRNA. Besides, we found that gRNA dimerization significantly impacts Pr55^Gag binding, and we confirmed that the internal loop of stem-loop 1 (SL1) in Psi is crucial for specific interaction with Pr55^Gag. Our analysis of gRNA fragments of different length supports the existence of a long-range tertiary interaction involving sequences upstream and downstream of the Psi region. This long-range interaction might promote optimal exposure of SL1 for efficient Pr55^Gag recognition. Altogether, our results shed light on the molecular mechanisms allowing the specific selection of gRNA by Pr55^Gag among a variety of svRNAs, all harboring SL1 in their first common exon.

BACKGROUND The novel coronavirus SARS-CoV-2 is responsible for the current global pandemic. There is a concerted effort within the global scientific community to identify (and thereby potentially mitigate) the possible modes of transmission through which the virus spreads throughout populations. OBJECTIVE Summarize the ways in which SARS-CoV-2 is transmitted and provide scientific support for the prevention and control of COVID-19. EVIDENCE AQUISITION We conducted an extensive literature search using electronic databases for scientific articles addressing SARS-CoV-2 transmission published from December 28, 2019 through July 31, 2020. We retrieved 805 articles, but only 302 were included and discussed in this review. The report captured relevant studies investigating three main areas: 1) viral survival, 2) transmission period and transmissibility, and 3) routes of viral spread. DEVELOPMENT Currently available evidence indicates that SARS-CoV-2 seems to have variable stability in different environments and is very sensitive to oxidants, such as chlorine. Temperature and humidity are important factors influencing viral survival and transmission. SARS-CoV-2 may be transmitted from person to person through several different routes. The basic mechanisms of SARS-CoV-2 transmission person-to-person contact through respiratory droplets, or via indirect contact. Aerosolized transmission is likely the dominant route for the spread of SARS-CoV-2, particularly in healthcare facilities. Although SARS-CoV-2 has been detected in non-respiratory specimens, including stool, blood and breast milk, their role in transmission remains uncertain. A complicating factor in disease control is viral transmission by asymptomatic individuals and through what would otherwise be understood as innocuous human activities. CONCLUSIONS This article provides a review of the published research regarding human-to-human transmission of SARS-CoV-2 and insights into developing effective control strategies to stop viral propagation.