Conserved regions 4.1 and 4.2 of sigma(70) constitute the recognition sites for the anti-sigma factor AsiA, and AsiA is a dimer free in solution.

The association of the bacteriophage T4-encoded AsiA protein with the final sigma(70) subunit of the Escherichia coli RNA polymerase is one of the principal events governing transcription of the T4 genome. Analytical ultracentrifugation and NMR studies indicate that free AsiA is a symmetric dimer and the dimers can exchange subunits. Using NMR, the mutual recognition sites on AsiA and final sigma(70) have been elucidated. Residues throughout the N-terminal half of AsiA are involved either directly or indirectly in binding to final sigma(70) whereas the two highly conserved C-terminal regions of final sigma(70), denoted 4.1 and 4.2, constitute the entire AsiA binding domain. Peptides corresponding to these regions bind tightly to AsiA individually and simultaneously. Simultaneous binding promotes structural changes in AsiA that mimic interaction with the complete AsiA binding determinant of final sigma(70). Moreover, the results suggest that a significant rearrangement of the dimer accompanies peptide binding. Thus, both conserved regions 4.1 and 4.2 are intimately involved in recognition of AsiA by final sigma(70). The interaction of AsiA with 4.1 provides a potential explanation of the differential abilities of DNA and AsiA to bind to free final sigma(70) and a mechanistic alternative to models of AsiA function that rely on binding to a single site on final sigma(70).

Herpes simplex virus DNA packaging sequences adopt novel structures that are specifically recognized by a component of the cleavage and packaging machinery.

The product of the herpes simplex virus type 1 U(L)28 gene is essential for cleavage of concatemeric viral DNA into genome-length units and packaging of this DNA into viral procapsids. To address the role of U(L)28 in this process, purified U(L)28 protein was assayed for the ability to recognize conserved herpesvirus DNA packaging sequences. We report that DNA fragments containing the pac1 DNA packaging motif can be induced by heat treatment to adopt novel DNA conformations that migrate faster than the corresponding duplex in nondenaturing gels. Surprisingly, these novel DNA structures are high-affinity substrates for U(L)28 protein binding, whereas double-stranded DNA of identical sequence composition is not recognized by U(L)28 protein. We demonstrate that only one strand of the pac1 motif is responsible for the formation of novel DNA structures that are bound tightly and specifically by U(L)28 protein. To determine the relevance of the observed U(L)28 protein-pac1 interaction to the cleavage and packaging process, we have analyzed the binding affinity of U(L)28 protein for pac1 mutants previously shown to be deficient in cleavage and packaging in vivo. Each of the pac1 mutants exhibited a decrease in DNA binding by U(L)28 protein that correlated directly with the reported reduction in cleavage and packaging efficiency, thereby supporting a role for the U(L)28 protein-pac1 interaction in vivo. These data therefore suggest that the formation of novel DNA structures by the pac1 motif confers added specificity on recognition of DNA packaging sequences by the U(L)28-encoded component of the herpesvirus cleavage and packaging machinery.

Stimulation of bacteriophage T4 middle transcription by the T4 proteins MotA and AsiA occurs at two distinct steps in the transcription cycle.

The bacteriophage T4 encodes proteins that are responsible for tightly regulating mRNA synthesis throughout phage development in Escherichia coli. The three classes of T4 promoters (early, middle, and late) are utilized sequentially by the host RNA polymerase as a result of phage-induced modifications. One such modification is the tight binding of the T4 AsiA protein to the sigma70 subunit of the RNA polymerase. This interaction is pivotal for the transition between T4 early and middle transcription, since it both inhibits recognition of host and T4 early promoters and stimulates T4 middle mode synthesis. The activation of T4 middle transcription also requires the T4 MotA protein, bound specifically to its recognition sequence, the "Mot box," which is centered at position -30 of these promoters. Accordingly, the two T4 proteins working in concert are sufficient to effectively switch the transcription specificity of the RNA polymerase holoenzyme. Herein, we investigate the mechanism of transcription activation and report that, while the presence of MotA and AsiA increases the initial recruitment of RNA polymerase to a T4 middle promoter, it does not alter the intrinsic stability of the discrete complexes formed. In addition, we have characterized the RNA polymerase-promoter species by UV laser footprinting and followed their evolution from open into initiating complexes. These data, combined with in vitro transcription assays, indicate that AsiA and MotA facilitate promoter escape, thereby stimulating the production of full-length transcripts.

The interaction between the AsiA protein of bacteriophage T4 and the sigma70 subunit of Escherichia coli RNA polymerase.

The AsiA protein of bacteriophage T4 binds to the sigma70 subunit of Escherichia coli RNA polymerase and plays a dual regulatory role during T4 development: (i) inhibition of host and phage early transcription, and (ii) coactivation of phage middle-mode transcription, which also requires the T4 DNA binding transcriptional activator, MotA. We report that the interaction between AsiA and sigma70 occurs with a 1:1 stoichiometry. When preincubated with RNA polymerase, AsiA is a potent inhibitor of open complex formation at the lac UV5 promoter, whereas it does not perturb preformed open or intermediate promoter complexes. DNase I footprinting and electrophoretic mobility shift analyses of RNA polymerase-DNA complexes formed at the T4 early promoter P15.0 show that AsiA blocks the initial RNA polymerase binding step that leads to the formation of specific closed promoter complexes. A contrasting result is obtained on the T4 middle promoter PrIIB2, where AsiA stimulates the formation of both closed complexes and open complexes. Therefore, we propose that AsiA modulates initial DNA binding by the RNA polymerase, switching promoter usage at the level of closed complex formation.

In vitro selection of packaging sites in a double-stranded RNA virus.

The Saccharomyces cerevisiae double-stranded RNA virus ScVL1 recognizes a small sequence in the viral plus strand for both packaging and replication. Viral particles will bind to this viral binding sequence (VBS) with high affinity in vitro. An in vitro selection procedure has been used to optimize binding, and the sequences isolated have been analyzed for packaging and replication in vivo. The selected sequence consists of a stem with a bulged A residue topped by a loop of several bases. Four residues of the 18 bases are absolutely conserved for tight binding. These all fall in regions that appear to be single stranded. Eight more residues have preferred identities, and six of these are in the stem. The VBS is similar to the R17 bacteriophage coat protein binding site. Packaging and replication require tight binding to viral particles.

Bacteriophage T4 MotA and AsiA proteins suffice to direct Escherichia coli RNA polymerase to initiate transcription at T4 middle promoters.

Development of bacteriophage T4 in Escherichia coli requires the sequential recognition of three classes of promoters: early, middle, and late. Recognition of middle promoters is known to require the motA gene product, a protein that binds specifically to the "Mot box" located at the -30 region of these promoters. In vivo, the asiA gene product is as critical for middle mode RNA synthesis as is that of the motA gene. In vitro, AsiA protein is known to loosen the sigma 70-core RNA polymerase interactions and to inhibit some sigma 70-dependent transcription, presumably through binding to the sigma 70 subunit. Here we show that, in vitro, purified MotA and AsiA proteins are both necessary and sufficient to activate transcription initiation at T4 middle promoters by the E. coli RNA polymerase in a sigma 70-dependent manner. AsiA is also shown to inhibit recognition of T4 early promoters and may play a pivotal role in the recognition of all three classes of phage promoters.

Healing of NSAID-induced gastric ulcers with a synthetic prostaglandin analog (enprostil).

OBJECTIVE: Conventional ulcer therapy has not been proven effective in healing gastric ulcers caused by nonsteroidal anti-inflammatory drugs (NSAIDs) if the NSAIDs are continued. Our objective in this study was to determine whether a prostaglandin analog is an effective treatment for such NSAID-induced lesions. METHODS: To make this determination, we conducted a 9-wk double-blind trial comparing placebo with enprostil 35 micrograms twice daily and three times daily. Use of antacids was not allowed. Three centers entered 145 patients with chronic inflammatory arthritis and osteoarthritis, mean age 63 yr, who required continuous fixed-dose NSAID therapy within the range of therapeutic dosage. The minimum entrance criterion was the presence of either four gastric erosions or one gastric ulcer. Two pretreatment endoscopies within a 2-wk interval were performed to establish the presence of stable baseline gastric lesions. Endoscopy was repeated at wk 6 and 9 during treatment. All groups were similar with regard to age distribution, sex, weight, height, smoking usage, and alcohol consumption. RESULTS: The ulcer healing rates were 14%, 57%, and 68% at 6 wk and 19%, 68%, and 74% at 9 wk for the groups receiving placebo, enprostil twice daily, and enprostil three times daily, respectively (p < 0.01). Complete mucosal healing of all erosions and ulcers at 9 wk occurred in 59% of enprostil-treated patients and in 10% of placebo-treated patients. Additional gastric erosions and gastric ulcers developed in 16% of placebo patients and 4% of the enprostil patients. Eighteen percent of enprostil patients withdrew early from the study due to adverse experiences, such as diarrhea and abdominal pain. CONCLUSION: We concluded that during continued NSAID therapy 1) enprostil 35 micrograms (taken either twice daily or three times daily) heals NSAID-induced gastric ulcers and erosions and protects the mucosa from further NSAID-induced gastric injury; 2) gastric ulcers and erosions rarely heal spontaneously, and 3) enprostil results in a high incidence of diarrhea.

Physical examination of musculoskeletal pain.

The authors present information on how to conduct an examination of musculoskeletal structures with the purpose of accurately locating the source of a patient's symptoms when musculoskeletal pathology is suspected. An accurate identification of the structure at fault will enable the physician to formulate a more specific and effective treatment program.

Anterior tarsal tunnel syndrome.

The pathogenesis, etiology, and diagnostic features of the anterior tarsal tunnel syndrome as it affects the foot are discussed in this manuscript.