Influence of cyclic AMP, agmatine, and a novel protein encoded by a flanking gene on speB (agmatine ureohydrolase) in Escherichia coli

Abstract

The speB gene of Escherichia coli encodes agmatine ureohydrolase (AUH), a putrescine biosynthetic enzyme. The speB gene is transcribed either from its own promoter or as a polycistronic message AMP (cAMP) repressed AUH activity of chromosomally encoded AUH but had no effect on plasmid-borne speB nor 4b(speB-phoA). It is concluded that ORF1 encodes a protein which is a posttranscriptional regulator of speB, agmatine induces speB independent of speA, and cAMP regulates speB indirectly.In Escherichia coli putrescine can be synthesized from arginine by decarboxylation of arginine to agmatine, catalyzed by arginine decarboxylase; agmatine is hydrolyzed to putrescine, catalyzed by agmatine ureohydrolase (AUH) (13). Arginine decarboxylase and AUH are encoded by the speA and speB genes, respectively, located at approximately minute 63.5 on the E. coli chromosome (1). We have sequenced the speB gene and characterized its pattern of transcription (12). The speB gene is encoded by one open reading frame (ORF); however, it can be transcribed as either a monocistronic or a polycistronic message. The speB promoter, initiating the monocistronic transcript, is unusual in that it does not require any sequence specificity upstream from the -10 Pribnow box for its activity. The polycistronic message is initiated from the promoter of speA residing immediately upstream from speB (12).The source of the speB gene was plasmid pKA5, which contains a 7.5-kb EcoRI fragment of E. coli chromosome subcloned into pBR322 (2). It had been previously established that this EcoRI fragment contains the speB, speA, and metK genes, encoding AUH, arginine decarboxylase, and methionine adenosyltransferase, respectively. In the initial search for the speB gene on pKA5, a 3.0-kb fragment subcloned into pBR322 resulted in overproduction of AUH activity (12). A small deletion at one end of this fragment caused a significant decrease in AUH activity. After establishing the location of the speB gene within the 3.0-kb fragment, it became apparent that the deletion did not map within the speB gene. Rather, the deletion included the 5' region of ORF1, the first of the two ORFs (ORF1 and ORF2) * Corresponding author. located on the strand complimentary to speB. These observations prompted us to investigate the nature of the relationship between ORF1, ORF2, and expression of speB. The data reported here indicate that ORF1 encodes a protein which stimulates expression of AUH at a posttranscriptional level.Agmatine is a substrate of the reaction catalyzed by AUH. A number of E. coli strains either bearing a chromosomal copy of speB or transformed with pKA5 show increased AUH activity following agmatine supplementation (9). Our results show that agmatine is an inducer of the speB, but not of the speA, promoter.The involvement of cyclic AMP (cAMP) in regulation of AUH in E. coli has been the subject of controversy. Halpern and Metzer (4) reported that cAMP supplementation of strain CS101B of E. coli K-12 induced the expression of AUH activity. In contrast, Satis...

Identification of regulatory network topological units coordinating the genome-wide transcriptional response to glucose in Escherichia coli

“…Genes encoding the integral membrane component of the flagellar export apparatus FliO ( fliO ) displayed a decrease in transcript levels. Putrescine synthesis in E. coli can proceed from the decarboxylation of arginine to agmatine and its subsequent hydrolysis to putrescine, reactions catalyzed by the products of genes speA and speB , respectively[24]. The higher transcript levels when growing in LB+G medium for potABD and speB encoding components of the spermidine/putrescine ATP-dependent importer and an enzyme of the putrescine biosynthetic pathway, respectively, are indicative of an increased demand for polyamines when conditions favor a higher growth rate for E. coli .…”

Small RNAs and Small Proteins Involved in Resistance to Cell Envelope Stress and Acid Shock in Escherichia coli : Analysis of a Bar-Coded Mutant Collection

“…SpeA and SpeB are required for the synthesis of polyamines (4), the presence of which has been shown to confer acid resistance to E. coli (40,55). The yqgB gene contains an internal promoter that drives expression of speA and speB (43). Therefore, deleting yqgB could eliminate speAB expression and render the yqgB mutant cells acid sensitive.…”

Klebsiella pneumoniae yggG Gene Product: A Zinc-Dependent Metalloprotease

“…The distinctive features of K. pneumoniae YggG suggest that this protein could be functionally different from Ste24p or HtpX. Comparison with its putative ortholog from E. coli [ 13 , 15 ] also revealed some differences in terms of the number of putative transmembrane domain and solubility. E. coli YggG was predicted to have an extra transmembrane domain at the N-terminus ( Figure 3 ) and it was reported to be membrane bound [ 15 ] whereas we have successfully expressed the K. pneumoniae YggG as a soluble protein.…”

“…This gene is highly conserved and its homologues could be found in various pathogenic microorganisms such as Shigella dysenteriae , Shigella flexneri , Salmonella typhimurium and Salmonella enterica . The gene was discovered in Escherichia coli when an open reading frame was found on the strand complementary to speB gene encoding agmatine ureohyrolase [ 13 ]. YggG is up regulated by heat shock and it interacts with Era protein, a membrane associated GTPase that is essential for E. coli viability [ 14 ].…”