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tRNAArg (fimU) and Expression of SEF14 and SEF21 in Salmonella enteritidis

ABSTRACT A Tn10 insertion affecting SEF14 fimbrial synthesis inSalmonella enteritidis was located 13 bp upstream of a gene designated fimU. The 77-bp DNA sequence of fimUfrom S. 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. fimUmapped to the SEF21 fim operon located 15 C’s from thesef14 gene cluster. Although fimU was located within the SEF21 fim gene cluster, the fimUTn10 insertion mutant of S. 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-borne fimUrestored 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.