Letovirinae

Letovirinae is a subfamily of the Coronaviridae family within the order Nidovirales. It encompasses divergent viruses that are related to coronaviruses but form a distinct lineage separate from the main Orthocoronavirinae and Torovirinae subfamilies. The subfamily was erected by the International Committee on Taxonomy of Viruses (ICTV) to accommodate virus lineages discovered in non-mammalian vertebrates and other hosts.

Taxonomy and hosts: Letovirinae currently includes at least one genus, Alphaletovirus, and has been detected in amphibians (especially anuran hosts) and fish. The exact number of species is subject to change as new discoveries are reported by ICTV committees.

Genome and replication: Like other nidoviruses, letoviruses possess single-stranded positive-sense RNA genomes of substantial length and use a replicase polyprotein encoded by ORF1ab with ribosomal frameshifting. They encode typical coronavirus-like structural proteins, but gene content and arrangement can differ from Orthocoronavirinae. Replication occurs in the cytoplasm with synthesis of a nested set of subgenomic RNAs.

Evolution and significance: Phylogenetic analyses indicate Letovirinae forms a deep-branching lineage within Nidovirales, providing clues about coronavirus evolution and host range expansion. Studying letoviruses helps illuminate how coronavirus-like replication programs evolved and adapted to diverse vertebrate hosts.

See also: Nidovirales, Coronaviridae, Orthocoronavirinae, Torovirinae.