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Structure/function analysis of ras using random mutagenesis coupled with functional screening assays
Abstract:
We review the use of functional assays for the ras protein, p21, that have allowed us to screen for mutant ras genes encoding proteins defective in either interactions with guanine nucleotides or transforming activity. GTP binding and GTP-dependent autokinase activities were assayed directly on lysed bacterial colonies expressing p21. Mutants encoding ras proteins deficient in these activities were isolated after randomly mutagenizing a v-rasH expression vector. Transformation defective mutants were isolated by randomly mutagenizing a v-rasH retroviral shuttle vector. NIH cells were then infected with a stock of nonreplicating mutagenized retroviruses and nontransformed infected colonies were isolated. The mutant ras genes were then rescued from these cells for analysis. Characterization of these mutants defines domains of p21 involved in both biochemical and biological activities and addresses the role of guanine nucleotide binding in p21 function.
Insights
Functional assays for ras proteins (p21) identified mutants affecting guanine nucleotide binding and transforming activity. This research defines key domains of p21 involved in biochemical and biological functions.
Area of Science:
- Molecular Biology
- Cellular Biology
- Biochemistry
Background:
- The ras protein (p21) plays a crucial role in cellular signaling pathways.
- Mutations in ras genes are frequently observed in various human cancers.
- Understanding ras protein function is vital for cancer research and therapeutic development.
Purpose of the Study:
- To review and detail the application of functional assays for screening ras protein (p21) mutants.
- To identify ras protein mutants with defects in guanine nucleotide interactions or transforming activity.
- To characterize these mutants to define functional domains of p21.
Main Methods:
- Functional assays were employed to assess GTP binding and GTP-dependent autokinase activities directly on bacterial colonies expressing p21.
- Random mutagenesis of a v-rasH expression vector and a v-rasH retroviral shuttle vector was performed.
- NIH cells were infected with mutagenized retroviruses, and nontransformed colonies were isolated to identify transformation-defective mutants.
Main Results:
- Mutant ras genes encoding proteins deficient in GTP binding or GTP-dependent autokinase activity were successfully isolated.
- Transformation-defective ras mutants were identified and rescued from infected NIH cells.
- Characterization of isolated mutants provided insights into domains critical for p21's biochemical and biological functions.
Conclusions:
- Functional assays are effective tools for screening ras protein mutants.
- The study defined specific domains of p21 essential for guanine nucleotide binding and transforming activity.
- This research contributes to understanding the role of guanine nucleotide binding in ras protein function and its implications in disease.