Nucleotide sequence of the rpsU-dnaG-rpoD operon from Salmonella typhimurium and a comparison of this sequence with the homologous operon of Escherichia coli.

In Escherichia coli the genes encoding ribosomal protein S21 (rpsU), DNA primase (dnaG), and the 70-kDal sigma subunit of RNA polymerase (rpoD) are contained in a single operon. These gene products are involved in the initiation of translation, DNA replication, and transcription, respectively. We have examined the homologous region in the closely related bacterium Salmonella typhimurium and have found that the same three genes are similarly organized. We have sequenced the DNA for this operon in S. typhimurium and have compared the (nt) nucleotide and amino acid (aa) sequences with E. coli. In the coding regions, the sequence conservation varies from extremely high for rpsU to moderate for dnaG with respect to both nt and aa sequence. In the noncoding regions, sequences thought to be important for the regulation of transcription are conserved, while other sequences are not conserved. aa differences in DNA primase and sigma are not randomly distributed and suggest regions that may be important for protein structure or function.