Adjust a FastA DNA genome file's ORFs to correct frameshifts by best Diamond match.

This is a simple script that corrects homopolymer stretches (e.g. GGGGGGGG) that putatively cause artifactual frameshifts in open reading frames of a prokaryotic genome. These false positive frameshifts are common in nanopore-derived genome assemblies, and the threshold for detection is based on that chemistry (homopolymers of 6bp+ for pore type R9.4). Frameshifts are corrected parsimoniously by adding or subtracting one base to restore the frame described by the best [Diamond] match against a provided protein database. The exception is if the parsimonious edit makes the homopolymer less than 6bp, in which case two bases are added to the homopolymer stretch to restore the reading frame. I would suggest running this script after other polishing methods such as nanopolish or Medaka.

This program assumes you have Diamond installed, and a local indexed copy of a protein database of some sort. I typically use UniRef90.

The program is a simple Perl script with no code dependencies, so once executable (e.g. chmod u+x framefix) it can be run like so:

./framefix nanopore_assembly.fasta 1e-25 output_prefix /path/to/uniref90/diamond_index

Where 1e-25 is the e-value threshold to consider a match evidence of a frameshift. Three output files are generated output_prefix.homopolymers_query.txt which lists the homopolymers and their genomic context that were submitted for inquiry to Diamond, output_prefix.diamond_nr.txt which is the best Diamond output for each of those queries (note that we are not doing taxonomic assignment with this code, so best hit is sufficient), and output_prefix.frameshift_adjusted.fna which has the parsimonious edits based on those Diamond matches applied to your input FastA genome file.