3.7. Orf7a
The number of amino acids of the orf7a of the SARS-CoV-2 and BatCoV RaTG13 are 121 amino acids while the orf7a of the SARS-CoV contains 122 amino acids (Table.1). The identity and similarity percentages of the orf7a of the SARS-CoV-2 and the SARS-CoV are 85.2 and 90.2 respectively. The orf7a of the SARS-CoV-2 and the BatCoV RaTG13 are with identity percentage of 97.5% and similarity percentage of 99.2% (Table.2).
The orf 7a of SARS-CoV is a trans-membrane protein divided into four regions from the N-terminal: 1) the first 15 amino acids is broken down by the infected host cells; 2) the amino acids 16-96 forms the intracellular domain; 3) the amino acids 97- 117 amino acids are transmembrane with hydrophobic nature; and 4) the C- terminal consists of the last five amino acids [43].
The orf7a plays a role in the binding and invasion of the virus to the host cells through interacting with the S, M, E, and the orf3a proteins [41,44]. The orf7a does not contribute for the replication of the virus [43-46]. The orf7a plays some functions in the host cells such as triggering of the apoptosis, down-regulation of protein synthesis, arrest of the cell cycle at the G0\G1 phase, and activation of the cytokine production [41,43,44,46].