tRNA Arg ( fimU ) and Expression of SEF14 and SEF21 in Salmonella enteritidis

A Tn10 insertion affecting SEF14 fimbrial synthesis inSalmonella enteritidis was located 13 bp upstream of a gene designatedfimU . The 77-bp DNA sequence offimU fromS. enteritidis was identical to that offimU encoding tRNAArg (UCU) fromSalmonella typhimurium and 96% identical to that of theEscherichia coli argU homolog. Furthermore, the open reading frame adjacent to and overlapping the 3′ end offimU was similar to the prophage DLP12 integrase gene. ThefimU -encoded transcript comigrated with total cellular tRNA and was predicted to form a tRNA-like cloverleaf structure containing the arginine anticodon UCU. Thus,fimU encoded a tRNAArg specific for the rare codon AGA.fimU mapped to the SEF21fim operon located 15 C’s from thesef14 gene cluster. AlthoughfimU was located within the SEF21fim gene cluster, thefimU Tn10 insertion mutant ofS. enteritidis was found to be defective in SEF14 as well as SEF21 (type 1) fimbria production. SEF17 and SEF18 fimbria production was not affected. Complementation of this mutant with plasmid-bornefimU restored normal production of the fimbrins SefA and FimA as well as their respective fimbriae SEF14 and SEF21. This is the first description of tRNA simultaneously controlling the production of two distinct fimbriae.