Forward and reverse chemical genetic

Thorpe DS. Forward and reverse chemical genetics using SPOS-based combinatorial chemistry. Comb. Chem. High T. Scr. 2003 6 623-647. Walsh DP, Chang YT. Chemical genetics. Chem. Rev. 2006 106 2476-2530. 

Kanoh, N., Honda, K, Simizu, S., Mmoi, M., Osada, H. (2005). Photo-cross-linked small-molecule affinity matrix for facilitating forward and reverse chemical genetics. Angew. Chem. Int. Ed., 44, 3559-3562. 

Forward and Reverse Chemical Genetics 308 Phenotypic Assays for Forward Chemical-Genetic Screening 311... 

Figure 1.1 Schematic overview of forward and reverse chemical genetics. In forward chemical genetics (left panel), a small molecule probe is discovered on the basis of its phenotypic effect the small molecule probe may then be subsequently used to identify the protein responsible for the phenotypic effect. In contrast, in reverse chemical genetics (right panel), a small molecule probe is discovered on the basis of its ability to modulate a specific protein the small molecule probe may then be used to modulate the cellular function of that specific protein, and the phenotypic effects that result.

Fig. 6-3 Forward versus reverse chemical molecules that can be used to probe the genetics. While forward chemical genetics function of the selected protein. Both relies on a phenotype of interest to guide the approaches require the use of small selection of biologically active small molecules and phenotypic assays but differ...

To summarize, as shown in Table 6-2, in a forward chemical-genetic screen, scientists start with a phenotype to find the protein or proteins responsible for it, and in a reverse chemical-genetic screen, the starting point is a protein of interest. Completing the trio of arrows in the discovery cycles in both cases provides valuable tools for the dissection of biological systems and mechanisms. 

In reverse genetics the aim is to start from a gene product (i.e. protein) of interest and determine what it does in a biological system. In the reverse chemical genetic variation, instead of using mutation to perturb the system, a small molecule is used. The kinds of chemicals suitable for this purpose are generally much the same as those described in Section 14.5.1 for forward chemical genetics for all the same reasons. 

In this section, the discovery of small molecules for the interrogation of biological mechanisms will be described. An appropriate small molecule tool may be discovered either on the basis of modulation of the activity of a specific protein (reverse chemical genetics. Section 1.3.1) or its phenotypic effect (forward chemical genetics. Section 1.3.2). Emphasis will be placed on the approaches that may be used to discover useful small molecule tools, and the insights into biological mechanisms that may be accrued. 

In eukaryotes, translation initiation is rate-limiting with much regulation exerted at the ribosome recruitment and ternary complex (elF2 GTP Met-tRNAjMet) formation steps. Although small molecule inhibitors have been extremely useful for chemically dissecting translation, there is a dearth of compounds available to study the initiation phase in vitro and in vivo. In this chapter, we describe reverse and forward chemical genetic screens developed to identify new inhibitors of translation. The ability to manipulate cell extracts biochemically, and to compare the activity of small molecules on translation of mRNA templates that differ in their factor requirements for ribosome recruitment, facilitates identification of the relevant target. 

Although the rates of spontaneous mutation are low, they can be greatly increased by mutagenic chemicals (Chapter 27) or by irradiation. It is perfectly practical to measure the rates of both forward and back mutation. When this was done, it was found that certain chemicals, e.g., acridine dyes, induce mutations that undergo reverse mutation at a very much lower frequency than normal. It was eventually shown that these mutations resulted either from deletions of one or more nucleotides from the chain or from insertions of extra nucleotides. Deletion and insertion mutations often result from errors during genetic recombination and repair at times when the DNA chain is broken. 

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