Cotranscription of two genes necessary for ribosomal protein L11 methylation (prmA) and pantothenate transport (panF) in Escherichia coli K-12

Abstract

Genetic complementation and enzyme assays have shown that the DNA region between panF, which encodes pantothenate permease, and orfl, the first gene of thefis operon, encodes prmA, the genetic determinant for the ribosomal protein Lll methyltransferase. Sequencing of this region identified one long open reading frame that encodes a protein of 31,830 Da and corresponds to the prmA gene. We found, both in vivo and in vitro, that prmA is expressed from promoters located upstream ofpanF and thus that the panF and prmA genes constitute a bifunctional operon. We located the major 3' end ofprmA transcripts 90 nucleotides downstream of the stop codon of prmA in the DNA region upstream of the fis operon, a region implicated in the control of the expression of thefis operon. Although no promoter activity was detected immediately upstream of prmA, Si mapping detected 5' ends of mRNA in this region, implying that some mRNA processing occurs within the bicistronic panF-prmA mRNA.Posttranslational modification of several ribosomal proteins is a general phenomenon observed in both prokaryotes and eukaryotes (2). Although much information on the expression of the genes for bacterial rRNAs and ribosomal proteins is available (29), little attention has been given to their posttranslational modifications, which are actually quite numerous. In Escherichia coli, proteins such as S5, S18, L12, and EF-Tu are acetylated at their N-terminal residues (L7 is the acetylated form of L12). Others modifications include addition of amino acids to the polypeptide chain, e.g., addition of one to four glutamic acid residues to the C terminal of ribosomal protein S6 (25,30). However, the most frequent modification is methylation. Several ribosomal proteins, e.g., Sli, L3, L7/L12, Lii, L16, and L33, as well as EF-Tu and IF3, have Nmethylated amino acids at specific positions (reviewed in reference 2). Lii is the most heavily methylated ribosomal protein, with three trimethylated amino acid residues: two Ns-trimethyllysines at positions 3 and 39 (19) and an aminoterminal 35). Methylation of ribosomal protein L 1I requires S-adenosyl-L-methionine as a methyl group donor (4) in a co-or posttranslational event.Mutations show that the prmA mutations result in loss of methyl groups from both the N-terminal alanine and the internal lysine residues (5, 14, 15). However, some residual Lii methyltransferase activity can be detected in extracts from strains carrying prmAl orprmA3 mutations (2,15). This residual activity could account for the lack of a phenotype associated with the prmA mutations. Since single mutations apparently result in the absence of both internal and N-terminal methyl groups from Li 1, it seems possible that the same enzyme is responsible for the methylation of all three amino acids. If this is the case, then the distinctive trimethylation of two different amino acids at three different loci when all of the other lysine residues of the protein are unmodified poses an interesting problem of enzyme specificity. We cannot, however, rule ou...

Arginine N-Methyltransferase 1 Is Required for Early Postimplantation Mouse Development, but Cells Deficient in the Enzyme Are Viable

“…5). The mouse protein also shares 45% overall identity with the Saccharomyces cerevisiae RMT1 enzyme (12) and 11% identity with the Escherichia coli L11 methyltransferase (34). This high degree of phylogenetic conservation was especially evident in regions containing consensus methyltransferase motifs (Fig.…”

hrcA, the first gene of the Bacillus subtilis dnaK operon encodes a negative regulator of class I heat shock genes

“…Here, the structure of the operon is identical to that of B. subtilis, but it is followed by an ORF called orf35. The deduced amino acid sequence of orf35 revealed 55% homology with the protein methyltransferase PrmA of E. coli, which is responsible for methylation of ribosomal protein L11 (34,35). In Clostridium acetobutylicum, the genomic organization of the dnaK operon is identical to that of B. subtilis, and here, too, dnaJ is followed by an ORF called orfB (3).…”

The dnaK operon of Bacillus subtilis is heptacistronic

“…In S. aureus and C. acetobutylicum, the region downstream of orf35/orfB has not yet been sequenced. Furthermore, the B. subtilis ORF35 exhibits significant homology to the ribosomal protein L11 methyltransferase encoded by prmA of E. coli (57% similarity, 32.5% identity) (42) and to the homologous PrmA protein of Haemophilus influenzae (54% similarity, 32% identity) (12).…”