ORF9b (formerly sometimes called ORF13) is a gene that encodes a viral accessory protein in coronaviruses of the subgenus Sarbecovirus, including SARS-CoV and SARS-CoV-2.

It has also sometimes been referred to as ORF9a, resulting in a downstream ORF of 76 codons in SARS-CoV, also overlapping with the N gene, being designated ORF9b.

[6] This fold switching behavior is also consistent with bioinformatics predictions and may also occur for the SARS-CoV homolog.

[2][3][8] Unlike its neighbor ORF9c, its length is well conserved in sarbecoviruses and there is strong evidence it is a functional protein-coding gene.

The SARS-CoV-2 protein has been reported to suppress interferon response via its interactions with Tom70, a component of the mitochondrial translocase of the outer membrane (TOM) complex.