The speB gene of Escherichia coli encodes the enzyme agmatine ureohydrolase (AUH). AUH catalyzes the hydrolysis of agmatine to urea and putrescine in one of the two polyamine biosynthetic pathways in E. coli. Sequencing of a 2.97-kilobase-pair fragment of the E. coli chromosome containing speB revealed the presence of three intact open reading frames (ORFs), ORF1 and ORF2 on one strand and ORF3 on the opposite strand, as weUl as a truncated ORF, ORF4, which terminated 92 kilobase pairs upstream from ORF3. ORF3 contained the coding sequence of the speB gene, as confirmed by complementation analysis. Two ORF3 transcripts were detected: a shorter transcript that included only ORF3 and a longer transcript that included both ORF3 and ORF4. The short transcript was abundantly expressed when the ORF4 sequences were deleted, but when ORF4 and its upstream sequences were present, the polycistronic message predominated and the amount of the monocistronic message was drastically reduced. The promoter from which the shorter transcript was produced contained a TATACT sequence at position -12, but sequences upstream from the -12 position seemed to be irrelevant for promoter activity. The predicted amino acid sequence of AUH contained three regions of high homology to the arginases of yeasts, rats, and humans.In Escherichia coli putrescine is synthesized either by decarboxylation of ornithine or by decarboxylation of arginine to agmatine followed by hydrolysis of agmatine to putrescine and urea (14). The last two reactions are catalyzed by the enzymes arginine decarboxylase and agmatine ureohydrolase (AUH), respectively. The AUH protein has previously been purified from an E. coli isolate that was transformed with the plasmid pKA5; the enzymatic properties of AUH have been characterized previously (9). The subunit size of AUH, as deduced from its mobility on a sodium dodecyl sulfate-polyacrylamide gel, is 38 kilodaltons. The expression of AUH activity is antagonistically regulated by cyclic AMP and agmatine. In the presence of the cyclic AMP receptor protein, cyclic AMP represses the expression of the speB gene, while agmatine induces it. These two modulators appear to act independently from each other (10); the mechanism of this differential regulation is unknown. The speB gene coding for AUH is located at approximately 63.5 min on the E. coli chromosome. Although a large chromosomal fragment corresponding to this region, including the speB gene, is present in the pKA5 plasmid, the exact location of speB was not previously established. Here we report the nucleotide sequence of the speB structural gene and identify the promoter responsible for transcription of one of two mRNAs encoding AUH. We also report the mapping of the mRNA resulting from transcription that initiated at this promoter. MATERIALS AND METHODSBacterial hosts, media, and growth conditions. E. coli CB806(A1acZ galK phoA8 rpsL thi recA56) (11) was used for all experiments involving the promoter vector pCB267 and its derivatives. E. coli DHSa [F- The bacteria wer...

Haemorrhagic enteritis virus (HEV) is a member of a genetically ill-defined group within the genus Aviadenovirus which causes significant clinical disease in gallinaceous fowl. Using DNA obtained from a low virulence isolate of HEV passed in turkeys, we developed a genomic restriction map and estimated an apparent genomic length of 25.5 kb. No evidence for extensive DNA hybridization was found between the HEV genome and either the hexon or penton base genes of human adenovirus 2 (HAdV-2) and fowl adenovirus 10 (FAdV-10). The HEV penton base gene was identified by PCR using primers based on conserved adenoviral DNA sequences. The penton base gene was expressed in Escherichia coli as a fusion protein and detected by anti-HEV serum in both colony and denaturing gel immunoblots. DNA sequencing revealed a putative penton base ORF with a predicted amino acid sequence showing approximately 39.0 %, 53.0 % and 44.2 % similarity with the penton base of HAdV-2, human adenovirus 40 (HAdV-40) and FAdV-10, respectively. The penton base gene was located at 43.3-48.6 m.u. on the HEV genome and had a remarkably low G + C content (33'8 %). DNA sequencing also revealed ORFs for putative core proteins resembling pVII, p-mu and a partial ORF similar to pVI (hexon-associated protein) of HAdV-2 and HAdV-40. The results support the claim that HEV represents a distinct group of viruses within the genus Aviadenovirus.