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Deletion in the 3' pol sequence correlates with aberration of RNA expression in certain replication-defective avian
Abstract:
The RNA expression of a series of replication-defective recovered avian sarcoma viruses (rASVs) were studied. Abnormal-sized viral RNAs, both larger and smaller than the genome, were observed in the nonproducer cells infected with rASVs containing env and pol deletions. Each nonproducer clone contained a single provirus integrated at a unique site and expressed a unique RNA pattern. Upon rescuing of the sarcoma virus with a helper virus and subsequent cloning, the RNA pattern of individual nonproducer clones again displayed variation according to the integration sites. This was not seen in nondefective rASV or in rASVs containing only an env deletion. The aberrant RNA expression did not result from the lack of reverse transcriptase activity per se, since neither nonconditional nor temperature-sensitive mutants of RSV expressed abnormal viral RNAs in the absence of a functional reverse transcriptase. The abnormal RNA patterns could not be corrected in trans by helper virus functions. The unusual-sized RNAs in env- pol- rASV-infected cells are not due to splicing to alternative acceptor sites for src mRNA because there are no extra viral sequences between the 5' leader and the src sequences; instead, they are due to the presence of extra sequences, most likely of cellular origin, at the 3' ends of the viral RNAs. Based upon the extent of deletions in the viral genomes, the data suggest that deletion in the 3' pol region of those rASVs results in a cis effect on the transcription and processing of the 3' ends of viral RNAs. The unusual-sized viral RNAs are most likely due to read-through transcription from the right-hand terminus of provirus into downstream cellular sequences, followed by cleavage and polyadenylation at multiple sites of the 3' region of the RNA transcripts. The extent of read-through transcription appears to depend on the chromosomal location of the provirus.
Insights
Replication-defective avian sarcoma viruses (rASVs) with env and pol deletions exhibit abnormal RNA expression. This is due to read-through transcription into cellular DNA, influenced by provirus integration site.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- Avian sarcoma viruses (ASVs) are retroviruses known to cause tumors in birds.
- Replication-defective ASVs (rASVs) are useful tools for studying viral gene expression and oncogenesis.
- Understanding viral RNA processing and expression is crucial for retroviral research.
Purpose of the Study:
- To investigate the RNA expression patterns of replication-defective rASVs with specific deletions.
- To determine the cause of abnormal viral RNA sizes observed in infected cells.
- To elucidate the role of viral genome deletions and provirus integration site in RNA expression.
Main Methods:
- Infection of nonproducer cells with various rASVs, including those with env and pol deletions.
- Analysis of viral RNA expression patterns using Northern blotting or similar techniques.
- Rescue experiments with helper viruses and cloning of viral progeny.
Main Results:
- rASVs with env and pol deletions produced abnormal-sized viral RNAs (larger and smaller than genomic RNA).
- RNA patterns varied among nonproducer clones, correlating with unique provirus integration sites.
- Abnormal RNA was not due to lack of reverse transcriptase activity or trans-complementation by helper virus.
- Unusual RNAs resulted from read-through transcription into cellular sequences at the 3' end, influenced by deletions in the pol region and provirus location.
Conclusions:
- Deletion in the 3' pol region of rASVs causes a cis effect on transcription and processing of viral RNAs.
- Abnormal RNA arises from read-through transcription into cellular sequences, with cleavage and polyadenylation at multiple sites.
- The extent of read-through transcription is dependent on the provirus's chromosomal integration site.