2,276 research outputs found
SecA mediates cotranslational targeting and translocation of an inner membrane protein
Protein targeting to the bacterial plasma membrane was generally thought to occur via two major pathways: cotranslational targeting by signal recognition particle (SRP) and posttranslational targeting by SecA and SecB. Recently, SecA was found to also bind ribosomes near the nascent polypeptide exit tunnel, but the function of this SecA–ribosome contact remains unclear. In this study, we show that SecA cotranslationally recognizes the nascent chain of an inner membrane protein, RodZ, with high affinity and specificity. In vitro reconstitution and in vivo targeting assays show that SecA is necessary and sufficient to direct the targeting and translocation of RodZ to the bacterial plasma membrane in an obligatorily cotranslational mechanism. Sequence elements upstream and downstream of the RodZ transmembrane domain dictate nascent polypeptide selection by SecA instead of the SRP machinery. These findings identify a new route for the targeting of inner membrane proteins in bacteria and highlight the diversity of targeting pathways that enables an organism to accommodate diverse nascent proteins
Carbon-Neutralized Joint User Association and Base Station Switching for Green Cellular Networks
Mitigating climate change and its impacts is one of the sustainable
development goals (SDGs) required by United Nations for an urgent action.
Increasing carbon emissions due to human activities is the root cause to
climate change. Telecommunication networks that provide service connectivity to
mobile users contribute great amount of carbon emissions by consuming lots of
non-renewable energy sources. Beyond the improvement on energy efficiency, to
reduce the carbon footprint, telecom operators are increasing their adoption of
renewable energy (e.g., wind power). The high variability of renewable energy
in time and location; however, creates difficulties for operators when
utilizing renewables for the reduction of carbon emissions. In this paper, we
consider a heterogeneous network consisted of one macro base station (MBS) and
multiple small base stations (SBSs) where each base station (BS) is powered by
both of renewable and non-renewable energy. Different from the prior works that
target on the total power consumption, we propose a novel scheme to minimize
the carbon footprint of networks by dynamically switching the ON/OFF modes of
SBSs and adjusting the association between users and BSs to access renewables
as much as possible. Our numerical analysis shows that the proposed scheme
significantly reduces up to 86% of the nonrenewable energy consumption compared
to two representative baselines.Comment: To appear in IEEE International Conference on Communications (ICC)
202
Timing and specificity of cotranslational nascent protein modification in bacteria
The nascent polypeptide exit site of the ribosome is a crowded environment where multiple ribosome-associated protein biogenesis factors (RPBs) compete for the nascent polypeptide to influence their localization, folding, or quality control. Here we address how N-terminal methionine excision (NME), a ubiquitous process crucial for the maturation of over 50% of the bacterial proteome, occurs in a timely and selective manner in this crowded environment. In bacteria, NME is mediated by 2 essential enzymes, peptide deformylase (PDF) and methionine aminopeptidase (MAP). We show that the reaction of MAP on ribosome-bound nascent chains approaches diffusion-limited rates, allowing immediate methionine excision of optimal substrates after deformylation. Specificity is achieved by kinetic competition of NME with translation elongation and by regulation from other RPBs, which selectively narrow the processing time window for suboptimal substrates. A mathematical model derived from the data accurately predicts cotranslational NME efficiency in the cytosol. Our results demonstrate how a fundamental enzymatic activity is reshaped by its associated macromolecular environment to optimize both efficiency and selectivity, and provides a platform to study other cotranslational protein biogenesis pathways
SELF-PRESENT BY AVATARS IN MULTIPLAYER ONLINE ROLE-PLAYING GAMES: THE INFLUENCE OF SELF-ESTEEM, ONLINE DISINHIBITION, AND SELF-DISCREPANCY
Playing Multiplayer Online Role-Playing Games (MMORPGs) is now a popular leisure activity for some people. Players spend significant energy and money on it. In MMORPGs, players can customize their avatars as virtual identities to present themselves in the virtual world. Avatars are important when playing MMORPGs. However, few previous studies focus on the psychological determinates for avatar presentation in MMORPGs. In this study, we used an online questionnaire of 337 participants to explore the antecedent factors influencing avatar presentation. The current study considers the influence of self-esteem, online disinhibition, and self-discrepancy on self-present and the influence of self-present on avatar presentation of idea self, stand out, and following a trend. The empirical survey result reveals the self-discrepancy between virtual and physical self are relative negatively with self-esteem and positive with online disinhibition. The self-present are influence by both self-discrepancy and online disinhibition. Besides, self-present perception will lead to avatar presentation. The current study provides contributions about confirming the antecedents of avatar presentation that may be serve as fundamental for future research on online game behavior
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