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Control of adenovirus major late gene expression at multiple levels
S Larsson1, C Svensson, G Akusjärvi
1Department of Microbial Genetics, Medical Nobel Institute, Karolinska Institute, Stockholm, Sweden.
Abstract:
Most late adenovirus (Ad) proteins are translated from mRNAs originating from the so-called major late transcription unit (MLTU). These mRNAs are grouped into five families (designated L1 to L5), where each family consists of mRNAs that have co-terminal 3' ends. We have used mutant and wild-type Ad infections to characterize levels at which major late gene expression is regulated. Our results suggest the existence of a novel intermediate stage during a lytic infection where mRNAs from regions L1 and L4 are selectively overexpressed compared to the L2, L3, and L5 mRNAs. Our data suggest that this RNA phenotype reflects the activity of the MLTU at a transient stage immediately following initiation of viral DNA replication. Early during an Ad infection only mRNA from region L1 accumulate. To efficiently accumulate mRNA from regions L1 and L5 both viral DNA replication and late protein synthesis were required. To allow for only viral DNA replication resulted in an extensive premature transcription termination and a preferential mRNA accumulation from regions L1 and L4. The surprising production of L4 mRNA under these conditions was not due to the activation of a novel r-strand promoter located in the vicinity of region L4 or due to a control at the level of RNA transport or stability. Instead our results indicate that in the absence of efficient late protein synthesis 3' end formation occurs preferentially at the L1 and L4 poly(A) addition sites.
Insights
Adenovirus (Ad) gene expression shows a novel intermediate stage during lytic infection. This stage selectively overexpresses L1 and L4 mRNAs, indicating regulation at the 3' end formation of major late transcription unit (MLTU) RNAs.
Area of Science:
- Molecular Biology
- Virology
- Gene Expression Regulation
Background:
- Adenovirus (Ad) late proteins are primarily translated from the major late transcription unit (MLTU).
- MLTU mRNAs are categorized into five families (L1-L5) with shared 3' ends.
- Understanding the regulation of Ad gene expression during lytic infection is crucial for viral replication studies.
Purpose of the Study:
- To investigate the regulatory mechanisms governing Ad major late gene expression during lytic infection.
- To identify novel intermediate stages in Ad gene expression.
- To elucidate the role of viral DNA replication and late protein synthesis in mRNA accumulation.
Main Methods:
- Utilizing mutant and wild-type Ad infections in cell culture.
- Analyzing mRNA levels from different regions of the MLTU.
- Comparing gene expression patterns under conditions with and without viral DNA replication and late protein synthesis.
Main Results:
- A novel intermediate stage was identified where L1 and L4 mRNAs are selectively overexpressed compared to L2, L3, and L5 mRNAs.
- This RNA phenotype correlates with the transient stage following initiation of viral DNA replication.
- In the absence of efficient late protein synthesis, 3' end formation preferentially occurred at L1 and L4 poly(A) sites, leading to L4 mRNA accumulation.
Conclusions:
- Ad gene expression exhibits a transient regulatory stage during lytic infection, immediately after viral DNA replication begins.
- Regulation occurs at the level of 3' end formation, specifically at the L1 and L4 poly(A) addition sites, in the absence of robust late protein synthesis.
- This finding provides new insights into the intricate control of Ad mRNA processing and accumulation.