The 16S ribosomal RNA, also known as 16S rRNA, is part of the 30S subunit. This 30S subunit is the small subunit of the 70S ribosome, which occurs in prokaryotes. Ribosomes are macromolecular complexes that facilitate protein synthesis. The 16S rRNA has a unique role, as it is crucial for initiating the translation by binding to the Shine-Dalgarno sequence. This sequence is generally located upstream of the start codon and complementary to a segment in the 16S rRNA. The genes coding for this crucial component of the ribosome are referred to as 16S rRNA genes. The 16S rRNA gene shows slow rates of evolution. These slow evolutionary rates make them valuable for phylogenetic reconstructions. Thus, the 16S rRNA gene can give valuable insights into phylogenetics, the evolution of life, and the investigation of the relationships between different organisms.
The full length of the 16S gene measures approximately 1500 bp. The highly conserved sequence comprises nine variable regions. Targeting only a few of these variable regions was previously done due to technological restrictions. Different primers were available to sequence only a subregion of the 16S gene using short-read sequencing. With the advancements in third-generation sequencing, the sequencing of the full length of the 16S gene is feasible.