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Identification and characterization of the in vitro synthesized gene products of bacteriophage M13
Abstract:
Bacteriophage M13 replicative form (RF) DNA was used to direct coupled transcription and translation in cell-free extracts prepared from Escherichia coli. By using RF DNA, isolated from cells infected with appropriate amber mutants of this phage, it has been possible to identify the products of genes I through IV. By using the same methods no gene-product relationship could be demonstrated for genes VI and VII. Coupled in vitro protein synthesis studies on RF-III DNA, a linear double-stranded DNA molecule, obtained after cleavage of either RF-I or RF-II DNA with the restriction endonuclease R.Hin11 from Haemophilus influenzae, indicated that the cleavage site for this enzyme is located in gene II. The in vitro products of both gene III and gene VIII are about 30 and six amino acids longer, respectively, than their native counterparts present within the virion. These results suggest that the latter proteins arise in vivo by cleavage of precursor molecules. Coupled transcription and translation studies on a DNA fragment which only contained the genetic information coding for gene IV protein, obtained after cleavage of RF DNA with the restriction endonuclease R.Hap11 from Haemophilus aphirophilus, indicated that a large number of the in vitro synthesized polypeptides are the result of premature chain termination.
Insights
Researchers identified bacteriophage M13 gene products using cell-free transcription and translation. Some M13 proteins appear to be processed from larger precursors, suggesting post-translational modification.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Bacteriophage M13 is a well-studied model organism for DNA replication and gene expression.
- Understanding phage gene function requires precise identification of protein products.
- Cell-free systems offer a controlled environment for studying transcription and translation.
Purpose of the Study:
- To identify the protein products of bacteriophage M13 genes using in vitro coupled transcription-translation.
- To investigate the processing and potential precursor forms of M13 proteins.
- To map restriction enzyme cleavage sites within the M13 genome.
Main Methods:
- Utilized cell-free extracts from Escherichia coli for coupled transcription and translation.
- Employed M13 replicative form (RF) DNA, including DNA from amber mutants.
- Used restriction endonucleases (R.Hin11, R.Hap11) to generate specific DNA fragments for analysis.
Main Results:
- Successfully identified the in vitro products for M13 genes I through IV.
- Determined that M13 gene products III and VIII are synthesized as larger precursors.
- Localized the R.Hin11 restriction enzyme cleavage site to gene II.
- Observed premature chain termination in in vitro synthesis of gene IV protein.
Conclusions:
- Established gene-product relationships for several bacteriophage M13 genes.
- Provided evidence for post-translational processing of M13 gene III and gene VIII proteins.
- Demonstrated the utility of cell-free systems for M13 molecular analysis.