Large deletions during retrovirus replication arose primarily during reverse transcription via mechanisms including misalignment and incorrect synthesis, potentially allowing acquisition of cellular genes.
This basic science study identifies novel mechanisms of large deletions during retroviral reverse transcription, including errors in strand transfer that can lead to the incorporation of cellular sequences.
Retroviruses mutate at a high rate during replication. We used a spleen necrosis virus-based vector system and helper cell line to characterize mutations occurring during a single round of retrovirus replication. The vector used, JD216HyNeo, codes for two drug resistance genes, hygromycin resistance (hygro) and neomycin resistance (neo). The downstream neo gene is expressed only when a mutation alleviates a block to splicing which is located in the upstream hygro gene. The mutations allowing splicing were large deletions, ranging in size from about 500 to about 2,000 bp. Most of the mutant proviruses lacked the encapsidation sequence, as shown by our inability to rescue the mutant proviruses with wild-type reticuloendotheliosis virus strain A and confirmed by Southern blotting and direct DNA sequence analysis. We therefore concluded that most of the deletions arose during reverse transcription in the target cell, rather than during transcription in the host cell. The sequence data also indicated that the deletions occurred by at least three different mechanisms: (i) misalignment of the growing point; (ii) incorrect synthesis and termination in the primer-binding sequence during synthesis of the plus-strand strong-stop DNA; and (iii) incorrect synthesis and termination before the primer-binding sequence during synthesis of the plus-strand strong-stop DNA. The second mechanism also led to the incorporation of cellular sequences into the proviral genome, pointing to a potential novel mechanism by which retroviruses can acquire cellular genes.
Pulsinelli et al. (Sun,) conducted a other in Retrovirus mutation. Spleen necrosis virus-based vector system (JD216HyNeo) was evaluated on Mechanisms of large deletions during retrovirus replication. Large deletions during retrovirus replication arose primarily during reverse transcription via mechanisms including misalignment and incorrect synthesis, potentially allowing acquisition of cellular genes.