Organization of the murE-murG region of Escherichia coli: identification of the murD gene encoding the D-glutamic-acid-adding enzyme

Abstract

The 2-min region of the Escherichia coli genome contains a large cluster of genes from pbpB to envA that code for proteins involved in peptidoglycan biosynthesis and cell division. From pLC26-6 of the collection of Clarke and Carbon (L. Clarke and J. Carbon, Cell 9:91-99, 1976) plasmids carrying different fragments from the 8-kilobase-pair region downstream of pbpB were constructed and analyzed for their ability to direct protein synthesis in maxicells, to complement various thermosensitive mutations, and to overproduce enzymatic activities. We report the localization of the previously unidentified murD gene coding for the D-glutamic acid-adding enzyme within this region. Our data show that the genes are in the order pbpB-murEmurF-X-murD-Y-murG, where X and Y represent chromosomal fragments from 1 to 1.5 kilobase pairs, possibly coding for unknown proteins. Furthermore, the murE and murF genes, encoding the meso-diaminopimelic acid and D-alanyl-D-alanine-adding enzymes, respectively, may be translationally coupled when transcription is initiated upstream of murE, within the preceding structural gene pbpB coding for penicillin-binding protein 3.

Variant tricarboxylic acid cycle in Mycobacterium tuberculosis : Identification of α-ketoglutarate decarboxylase

“…The combined value, which was assessed enzymatically in total cell lysates, was far higher than what we detected by physical methods in the methanol extract of the soluble fraction of the cell lysate. The levels of glutamate detected in Mtb in the present work, which are estimated to correspond to 665 mol͞g dry weight (log phase) and 207 mol͞g dry weight (stationary phase), are within or above the higher values reported for E. coli (18), comparable to those in Bacillus subtilis (43) and in the lower range of values reported for Corynebacterium glutamicum (44). Conversion of these levels to intracellular concentrations depends on measurement of cell water content, which has apparently not been done for Mtb.…”

“…Conversion of these levels to intracellular concentrations depends on measurement of cell water content, which has apparently not been done for Mtb. For purposes of approximation, use of cell volumes estimated for other bacteria such as E. coli (18), Bacillus subtilis (43), and Clostridium perfringens (19) would suggest that Mtb's intracellular glutamate concentration may be on the order of 80 mM. However, Mtb's smaller size (45) and higher lipid content (see Materials and Methods) support estimates of intracellular glutamate concentration ranging from Ϸ80 mM to the low molar level.…”

Homology among MurC, MurD, MurE and MurF proteins in Escherichia coli and that between E. coli MurG and a possible MurG protein in Bacillus subtilis.

“…The open reading frame for murG contains two possible start codons, ATG (82-84) and ATG (106-108), for encoding peptides of 355 and 347 amino acid residues (mol wt 37,814 and 36,956), respectively, but the N-terminal amino acid sequence of the MurG protein has not been determined. Identification of the MurD, MurE and MurF proteins has been reported (14,17) and a 38,000 molecular weight protein was suggested as one of the candidates for the murG product (17).…”

“…Also subsequently located in the mra region were: the gene pbpB [also called ftsl (20)], which codes for penicillin-binding protein 3, a septum-peptidoglycan synthetase (10); ftsW, which also functions in the septum formation (9); and murG, which produces a protein of unidentified function involved in the cell growth (25). Through the recent studies of Ishino et al (9), Ikeda et al (6)(7)(8), and others (14,17,21), the total mra region covering a 12 kb chromosomal fragment close upstream from ftsl to ddl has been physically mapped; and determination of its base sequence has been completed: ftsl (20), murE (18b, 28), murF (21), mra Y (ref. 7 and M. Ikeda et al, submitted for publication), murD (7,16), ftsW (6), murG (8,18a), murC (8) and ddl (24).…”

The murG gene of the Escherichia coli chromosome encoding UDP-N-acetylgluco-samine: undecaprenyl-pyrophosphoryl-N-acetylmuramoyl-pentapeptide N-acetylglucosaminyl transferase.

“…UDP N-acetyl-muramyl-pentapeptide (UDP-MurNAc-L-AIa-D-Glu-meso-A2pm-D-AIa-D-Ala) syn-thesis from UDP-MurNAc (5,(9)(10)(11)(12); and mraY encodes the enzyme for the first step of lipid-cycle reactions, UDP-MurNAc-pentapeptide: undecaprenyl-phosphate phospho-MurNAc-pentapeptide transferase (6). The function of only murG is unknown, but previous studies showed that its mutation caused cell lysis (14).…”