Table 1. The 20 feature sets generated from the four representations of the viral genomes.

Genome representation	[Letter set] (Alphabet size)	K-mers lengths tested (k)	Feature set size for maximum k
DNA	[A,C,G,T] (4)	[1–9]	262,144
AA	[Amino Acid single letter code] (20)	[1–4]	160,000
PC	[t-z] (7)	[1–6]	117,649
Domains	[All domains predicted within each dataset]	1	Total number of unique domains in all the viral genomes in VHDB—2200

Genome representation: DNA—nucleotide sequence; AA—amino acid sequence of CDS regions; PC—physio-chemical properties, each amino acid residue binned into one of seven bins based on its physio-chemical property; Domains—presence of PFAM domain in the sequence.