Are primer sets with the names “515F/806R” and “U515F/806R” exactly the same? I can find all kinds of mentions of one or the other, but haven’t been able to find them both in the same document. The closest I’ve come to finding them both in the same document is finding an article having one notation and some of its references having the other.
The numbers refer to positions on the 16S gene: A forward primer around 515 and a reverse primer around 806, which is the expected location of the variable region 4 on the 16S gene.
The U stands for ‘Universal’ because these primers are designed to be ‘universal’ across all microbes.
So, yeah, both these terms refer to the same region: 16S V4
The region might be the same, but the primer sets that target the V4 region could be different! For example, the Earth Microbiome Program lists both the old and new primers they used to target this region, and other teams use other primers.
I hope this helps! Let me know if you have other questions