1,344 research outputs found
Neutral genetic drift can aid functional protein evolution
BACKGROUND: Many of the mutations accumulated by naturally evolving proteins
are neutral in the sense that they do not significantly alter a protein's
ability to perform its primary biological function. However, new protein
functions evolve when selection begins to favor other, "promiscuous" functions
that are incidental to a protein's biological role. If mutations that are
neutral with respect to a protein's primary biological function cause
substantial changes in promiscuous functions, these mutations could enable
future functional evolution.
RESULTS: Here we investigate this possibility experimentally by examining how
cytochrome P450 enzymes that have evolved neutrally with respect to activity on
a single substrate have changed in their abilities to catalyze reactions on
five other substrates. We find that the enzymes have sometimes changed as much
as four-fold in the promiscuous activities. The changes in promiscuous
activities tend to increase with the number of mutations, and can be largely
rationalized in terms of the chemical structures of the substrates. The
activities on chemically similar substrates tend to change in a coordinated
fashion, potentially providing a route for systematically predicting the change
in one function based on the measurement of several others.
CONCLUSIONS: Our work suggests that initially neutral genetic drift can lead
to substantial changes in protein functions that are not currently under
selection, in effect poising the proteins to more readily undergo functional
evolution should selection "ask new questions" in the future
Contexts of Cultural Diversity Professional Development in Schools
This report is part of a larger MERC study on Professional Development for Success in Culturally Diverse Schools.The goals of the larger study are (1) to understand the landscape of diversity within the schools in the MERC region, (2) to consider the implications for school policy and professional practice, (3) to review the current models of professional development that support teachers and other school professionals in regards to issues of cultural diversity, and (4) to develop and test models of professional development that have positive impacts on teacher practice, student outcomes and overall school success. With these goals in mind, this report contains three parts. Part 1 discusses demographic changes in the MERC region and provides historical, political, social, and economic contexts for understanding these changes. Part 2 describes the federal, state, and local policy contexts relevant to cultural diversity within schools, and professional development (PD) related to this topic. This section also reviews research on how policy contexts shape teachers’ decisions to participate in PD. Part 3 reviews existing studies of cultural diversity PD and describes the types of PD programs currently available in the MERC region. In the conclusion to the report, we present a list of recommendations for policy and and for future development and implementation of PD related to cultural diversity. The final section of the report also describes gaps in the existing body of knowledge and the research needed to better understand PD related to cultural diversity
Plasmonic Enhancement of Emission from Si-nanocrystals
Plasmonic gratings of different periodicities are fabricated on top of
Silicon nanocrystals embedded in Silicon Dioxide. Purcell enhancements of up to
2 were observed, which matches the value from simulations. Plasmonic
enhancements are observed for the first three orders of the plasmonic modes,
with the peak enhancement wavelength varying with the periodicity. Biharmonic
gratings are also fabricated to extract the enhanced emission from the first
order plasmonic mode, resulting in enhancements with quality factors of up to
16.Comment: 4 pages, 5 figures added explanation of low purcell enhancement
updated figure
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