In the E.coli 70S ribosome in the initiation state (PubMed:12809609) it has been modeled to contact the 23S rRNA of the 50S subunit forming part of bridge B1a; this bridge is broken in the model with bound EF-G. The 23S rRNA contact site in bridge B1a is modeled to differ in different ribosomal states (PubMed:12859903), contacting alternately S13 or S19. In the 3.5 angstroms resolved ribosome structures (PubMed:16272117) the contacts between L5, S13 and S19 bridge B1b are different, confirming the dynamic nature of this interaction. Bridge B1a is not visible in the crystallized ribosomes due to 23S rRNA disorder. Protein S19 forms a complex with S13 that binds strongly to the 16S ribosomal RNA. Contacts the A site tRNA. Part of the 30S ribosomal subunit (PubMed:348496, PubMed:3279034, PubMed:10094780, PubMed:12244297, PubMed:12809609, PubMed:12859903, PubMed:16272117, PubMed:27934701, PubMed:27906160, PubMed:27906161). Binds S13 and L5 and cross-links to the A site tRNA (PubMed:12809609, PubMed:16272117, PubMed:12859903). Belongs to the universal ribosomal protein uS19 family.