What are the four amino acids in the SARS-CoV-2 spike protein?

"Gary Whittaker, PhD, Professor of Virology, is the senior author on the study, which identifies a structural loop in the SARS-CoV-2 spike protein, the area of the virus that facilitates entry into a cell, and a sequence of four amino acids in this loop that is different from other known human coronaviruses in this viral lineage"
http://www.bioquicknews.com/node/5321

"The addition of a four amino acid insertion, PRRA, in the receptor-binding domain of the SARS-CoV-2 spike protein added a furin cleavage site."
https://www.scienceboard.net/index.aspx?sec=sup&sub=BioChem&pag=dis&ItemID=1014

"Two notable features have been identified in the SARS-CoV-2 genome: (1) the receptor binding domain of SARS-CoV-2; (2) a unique insertion of twelve nucleotide or four amino acids (PRRA) at the S1 and S2 boundary"
https://nanoporetech.com/resource-centre/identification-common-deletion-spike-protein-sars-cov-2

"The spike protein of SARS-CoV-2 has a very special feature, a segment of four amino acids called a furin cleavage site."

"There are several published papers showing that this four-amino acid sequence furin cleavage site is missing from the closest relatives of SARS-CoV-2 and has been inserted in precisely the best place in the spike protein to give it the ability to become highly infectious."

"This unique amino acid combination means that SARS-CoV-2 is considerably more infectious than related coronaviruses. It also explains why the virus infects multiple organs and attacks the nervous systems.9,10

It is doubtful that this recombination of two viruses, plus the insertion of the most efficient multi-basic cleavage site in precisely the best place on the spike protein, happened naturally. Nothing close to this combination has been found in nature. It is more likely to have been constructed in a laboratory through Gain-of-Function research.

This type of complex combination would need many decades to evolve to the current structure to infect the first humans, and then evolve further to be highly infectious to humans."
https://www.organicconsumers.org/blog/covid-19-spike-and-furin-cleavage

"Early characterizations of the SARS-CoV-2 genome revealed the existence of a distinct four amino acid insert within the spike (S) protein (underlined, SPRRAR↓S), at the S1/S2 site located at the interface between the S1 receptor binding subunit and the S2 fusion subunit."
https://www.cell.com/iscience/fulltext/S2589-0042(20)30397-7