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Expression of early genes of origin-defective mutants of simian virus 40
Abstract:
The nucleotide sequences of eight origin-defective mutants of simian virus 40 have been determined. All of the mutants have suffered deletions, which range in size from 4 to 241 nucleotides. Some of the mutants induce the synthesis of tumor (T) antigen, others do not. Viral mRNA extracted from rat cells transformed by two of the T-antigen-positive mutants has been analyzed by the S1 nuclease technique of Berk and Sharp. Irrespective of the size or the location of the deletions, the 5' ends of viral mRNAs are located approximately the same distance from the A+T-rich region (A-T-T-T-A-T) rather than at a specific site in the viral genome.
Insights
Simian virus 40 mutants with deletions were sequenced. Viral mRNA starts near the A+T-rich region, regardless of deletion size or location, indicating its importance for viral gene expression.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Simian virus 40 (SV40) is a well-studied model organism for eukaryotic DNA replication and gene expression.
- Origin-defective mutants are crucial for understanding viral DNA replication initiation.
- Tumor (T) antigen plays a key role in SV40 replication and transformation.
Purpose of the Study:
- To determine the nucleotide sequences of eight origin-defective SV40 mutants.
- To analyze the impact of deletions on viral mRNA synthesis and T-antigen production.
- To identify the precise transcription start sites of viral mRNA in relation to genomic features.
Main Methods:
- DNA sequencing of eight SV40 origin-defective mutants.
- Analysis of viral mRNA using the S1 nuclease technique (Berk and Sharp).
- Culturing of rat cells transformed by SV40 mutants.
Main Results:
- All eight mutants contained deletions ranging from 4 to 241 nucleotides.
- Some mutants produced T-antigen, while others did not.
- The 5' ends of viral mRNAs were consistently located near the A+T-rich region (A-T-T-T-A-T), irrespective of deletion size or location.
Conclusions:
- Deletions in the SV40 genome affect origin function but do not alter the primary transcription start site.
- The A+T-rich region is a critical determinant for the initiation of viral mRNA transcription.
- This finding provides insights into the regulation of gene expression in DNA viruses.