Summary auto-generated
This study identified and characterized homologous regions (hrs) in the Spodoptera exigua multicapsid nucleopolyhedrovirus (SeMNPV) genome. Researchers found six dispersed hrs (Sehr1–Sehr6) containing palindromic repeats and other regulatory sequences. Each hr contained 1–9 palindromic repeats of 68 bp, significantly larger than the 28 bp repeats found in other baculoviruses like AcMNPV. All six hrs replicated efficiently in SeMNPV-infected insect cells during transient DNA replication assays. Notably, SeMNPV hrs showed high specificity—they did not replicate when AcMNPV was the helper virus, and conversely, AcMNPV hrs failed to replicate with SeMNPV. This contrasts with the non-hr type origin of replication identified earlier, which replicated with both viruses. The palindromic repeats showed no sequence homology to hrs from other baculoviruses despite structural similarity. These findings suggest that SeMNPV DNA replication is a highly specific process, with the unique palindromic repeat sequences potentially serving as recognition elements for virus-specific replication factors.
Key findings
- Six homologous regions (Sehr1–Sehr6) dispersed throughout the SeMNPV genome contain 68 bp palindromic repeats distinct from those in other baculoviruses
- All Sehr-containing plasmids replicated in SeMNPV-infected cells, with even a single palindromic repeat being sufficient for replication activity
- SeMNPV hrs exhibit high specificity and do not replicate in AcMNPV-infected cells, nor do AcMNPV hrs replicate with SeMNPV
- SeMNPV hrs contain multiple putative transcription factor binding sites and regulatory sequences, suggesting dual roles in DNA replication and transcriptional enhancement
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Abstract
The region upstream of the Spodoptera exigua multicapsid nucleopolyhedrovirus (SeMNPV) ubiquitin gene contains four near- identical 68-bp-long palindromic repeats. This region, named Sehr6 and located at map unit (m.u.) 88 of the SeMNPV genome on pSeEcoRI-2.2, showed structural homology to previously identified homologous regions (hrs) in a number of other baculoviruses. Hrs function as enhancers of transcription and as putative origins (oris) of baculovirus DNA replication. Five additional hrs (Sehr1-Sehr5) were identified on the SeMNPV genome by Southern blot hybridization with an 18-bp-long oligonucleotide complementary to a sequence conserved within the arms of the four palindromic repeats of Sehr6. Sehr1-Sehr6 were dispersed on the SeMNPV genome at m.u. 8.0, 30.0, 38.5, 51.0, 77.0 and 88.0, respectively. Sequence analysis of these hrs confirmed the presence of palindromic repeats, highly similar to those found in pSeEcoRI-2.2. The number of palindromes varied from one (Sehr4) to nine (Sehr1) per hr. The Sehrs are all present in non-coding regions of the SeMNPV genome and also contain multiple putative transcription recognition sequences. Plasmids containing either of the Sehrs replicated in an SeMNPV- dependent DNA replication assay. The Sehrs were unable to replicate in an AcMNPV-dependent DNA replication assay. This was in contrast to the previously observed SeMNPV non-hr type ori, which replicated in the presence of both AcMNPV and SeMNPV. These data suggest that the replication of SeMNPV and the role of hrs in this process is highly specific.