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Regulation of integrated adenovirus sequences during adenovirus infection of transformed cells
Abstract:
A human cell line (293) transformed by adenovirus type 5 encodes mRNA's and proteins from the early region 1 (E1) of the viral genome. These products correspond to those synthesized early after adenovirus infection of normal cells. This pattern of expression is different from that observed at later times in the lytic cycle. We have determined whether integrated sequences can undergo the early-late transition during infection of transformed cells. Cultures of 293 cells were infected with mutants of adenovirus type 5 that have deletions in EI genes. In such infections, the integrated sequence complements the deletion mutants so that viral DNA replication, late mRNA and protein synthesis, and viral assembly occur. Because the infecting genomes lack EI sequences, the products synthesized from the integrated DNA could be analyzed. In contrast to the early-late transition that occurs with EI DNA in free viral genomes, the pattern of mRNAs and proteins made from the integrated sequences was restricted to the early pattern. Assuming that the viral sequences in 293 cells have not become altered during the history of the cells, our results suggest that regulation of integrated adenovirus genes may not be determined exclusively by nucleotide sequence recognition. Apparently, during infection certain factors prevent the integrated viral genes from responding to the regulatory signals which control late expression from free EI DNA. The distinction between integrated and free viral sequences might reflect the different fates of viral and host transcripts during the lytic cycle of adenovirus.
Insights
Integrated adenovirus genes in 293 cells do not switch to late gene expression during infection. This suggests that regulation of integrated viral genes involves more than just DNA sequence recognition.
Area of Science:
- Molecular Virology
- Cell Biology
- Genetics
Background:
- Human 293 cells, transformed by adenovirus type 5, express early region 1 (E1) viral mRNAs and proteins.
- This expression mimics early adenovirus infection but differs from later stages of the lytic cycle.
Purpose of the Study:
- To investigate if integrated viral DNA sequences can transition from early to late gene expression during infection of transformed cells.
- To understand the regulatory mechanisms governing integrated adenovirus gene expression.
Main Methods:
- Infection of 293 cells with adenovirus type 5 mutants lacking E1 genes.
- Analysis of viral mRNA and protein synthesis from integrated sequences in the presence of complementing viral genomes.
Main Results:
- Integrated adenovirus sequences in 293 cells remained restricted to early gene expression patterns, even when viral DNA replication and late protein synthesis occurred.
- The early-to-late transition observed with free viral genomes did not happen for integrated sequences.
Conclusions:
- Regulation of integrated adenovirus genes is not solely dependent on DNA sequence recognition.
- Factors present during infection may prevent integrated viral genes from responding to late expression signals, potentially due to differences in viral and host transcript fates.