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What's the point?
Wu et al. showed recombination between COVID-19 and bat coronaviruses located within the S-gene. We want to confirm this observation and provide a publicly accessible workflow for recombination detection.
In previous coronavirus outbreaks (SARS), retrospective analyses determined that adaptive substitutions might have occurred in the S-protein Zhang et al., e.g., related to ACE2 receptor utilization. While data on COVID-19 are currently limited, we investigated whether or not the lineage leading to them showed any evidence of positive diversifying selection.
We employ a recombination detection algorithm (GARD) developed by Kosakovsky Pond et al. and implemented in the
hyphy package. To select a representative set of S-genes we perform a blast search using the S-gene CDS from NC_045512 as a query against the
nr database. We select coding regions corresponding to the S-gene from a number of COVID-19 genomes and original SARS isolates. This set of sequences can be found in this repository
We then generate a codon-based alignment using the workflow shown below and perform the recombination analysis using the
gard tool from the
For selection analyses, we apply the Adaptive Branch Site Random Effects method to test whether or each branch of the tree shows evidence of diversifying positive selection along a fraction of sites using the
absrel tool from the
A set of unaligned CDS sequences for the S-gene.
A recombination report:
and a map of possible recombination hotspots:
A selection analysis summary and tree (COVID-19 isolate is MN988668_1)
and a plot of the inferred ω distribution for the MN988668_1 branch.
History and workflow
A Galaxy workspace (history) containing the most current analysis can be imported from here.
The publicly accessible workflow can be downloaded and installed on any Galaxy instance. It contains version information for all tools used in this analysis.
The workflow takes unaligned CDS sequences, translates them with
EMBOSS:tanseq, aligns translations using
mafft, realigns original CDS input using the mafft alignment as a guide and sends this codon-based alignment to
Tools used in this analysis are also available from BioConda:
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Created: 25th Mar 2020 at 10:05
Last updated: 25th Mar 2020 at 11:23