Last Updated on July 14, 2023
Clustal Omega is a general purpose multiple sequence alignment (MSA) program for protein and DNA/RNA. It produces high quality MSAs and is capable of handling data-sets of hundreds of thousands of sequences in reasonable time.
In default mode, users give a file of sequences to be aligned and these are clustered to produce a guide tree and this is used to guide a “progressive alignment” of the sequences. There are also facilities for aligning existing alignments to each other, aligning a sequence to an alignment and for using a hidden Markov model (HMM) to help guide an alignment of new sequences that are homologous to the sequences used to make the HMM. This latter procedure is referred to as “external profile alignment” or EPA.
Clustal-Omega uses HMMs for the alignment engine, based on the HHalign package from Johannes Soeding. Guide trees are made using an enhanced version of mBed which can cluster very large numbers of sequences in O(N*log(N)) time. Multiple alignment then proceeds by aligning larger and larger alignments using HHalign, following the clustering given by the guide tree.
In its current form Clustal-Omega has been extensively tested for protein sequences, DNA/RNA support has been added since version 1.1.0.
Clustal-Omega accepts 3 types of sequence input: (i) a sequence file with un-aligned or aligned sequences, (ii) profiles (a multiple alignment in a file) of aligned sequences, (iii) a HMM.
Clustal Omega is currently a command line-only tool.
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