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Fitness analyses of all possible point mutations for regions of genes in yeast

Abstract

Deep sequencing can accurately measure the relative abundance of hundreds of mutations in a single bulk competition experiment, which can give a direct readout of the fitness of each mutant. Here we describe a protocol that we previously developed and optimized to measure the fitness effects of all possible individual codon substitutions for 10-aa regions of essential genes in yeast. Starting with a conditional strain (i.e., a temperature-sensitive strain), we describe how to efficiently generate plasmid libraries of point mutants that can then be transformed to generate libraries of yeast. The yeast libraries are competed under conditions that select for mutant function. Deep-sequencing analyses are used to determine the relative fitness of all mutants. This approach is faster and cheaper per mutant compared with analyzing individually isolated mutants. The protocol can be performed in 4 weeks and many 10-aa regions can be analyzed in parallel.

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Figure 1: Bulk competition of libraries of point mutants in yeast.
Figure 2: Steps to generate plasmid libraries of point mutants.
Figure 3: Steps to prepare DNA for deep sequencing.
Figure 4: Analysis pipeline for measuring fitness effects of mutations from deep-sequencing data.

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Acknowledgements

This work was supported in part by grants from the US National Institutes of Health (R01-GM083038) and the American Cancer Society (RSG-08–17301-GMC) to D.N.A.B.

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Authors and Affiliations

Authors

Contributions

R.H., B.R., L.J. and D.N.A.B. all contributed to the development and optimization of the protocol and writing the article. R.H. prepared the initial draft for the section on generating mutant libraries. B.R. prepared the initial draft for the section on growth competition. B.R. and L.J. prepared the initial draft for the section on preparing samples for deep sequencing. D.N.A.B. prepared the initial draft for the section on processing sequencing data. D.N.A.B. supervised the work and prepared the final version of the manuscript.

Corresponding author

Correspondence to Daniel N A Bolon.

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Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

Features and sequence of bacterial-yeast shuttle plasmid pRNDM. This plasmid was derived from pRS414 with the tryptophan marker replaced by KanMX4 and the beta-lactamase gene removed. (PDF 48 kb)

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Hietpas, R., Roscoe, B., Jiang, L. et al. Fitness analyses of all possible point mutations for regions of genes in yeast. Nat Protoc 7, 1382–1396 (2012). https://doi.org/10.1038/nprot.2012.069

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