Identification of an additional member of the secretin superfamily of proteins in Pseudomonas aeruginosa that is able to function in type II protein secretion

Pseudomonas aeruginosa is a prolific exporter of virulence factors and contains three of the four protein secretion systems that have been described in Gram-negative bacteria. The P. aeruginosa type II general secretory pathway (GSP) is used to export the largest number of proteins from this organism, including lipase, phospholipase C, alkaline phosphatase, exotoxin A, elastase and LasA. Although these exoproteins contain no sequence similarity, they are specifically and efficiently transported by the secretion apparatus. Bacterial homologues of XcpQ (GspD), the only outer membrane component of this system, have been proposed to play the role of gatekeeper, by presumably interacting and recognizing the exported substrates to allow their passage through the outer membrane. While determining the phenotype of non-polar deletions in each of the xcp genes, we have shown that a deletion of the P. aeruginosa strain K xcpQ does not completely abolish protein secretion. As the proposed function of XcpQ should be requisite for secretion, we searched for additional factors that could carry out this role. A cosmid DNA library from a PAK strain deleted for xcpP-Z was tested for its ability to increase protein secretion by screening for enhanced growth on lipid agar, a medium that selects for the secretion of lipase. In this manner, we have identified an XcpQ homologue, XqhA, that is solely responsible for the residual export observed in a Δ xcpQ strain, although it is not required for efficient secretion in wild-type P. aeruginosa . We have also demonstrated that this protein is capable of recognizing all of the exoproteins of P. aeruginosa , arguing against the proposed role of members of the secretin family as determinants of specificity.     

The ets sequence is required for induction of erythroblastosis in chickens by avian retrovirus E26.

E26 is a replication-defective avian retrovirus that causes an erythroblastic leukemia in vivo and transforms hematopoietic precursor cells of both the erythroid and the myeloid lineages in vitro. The E26 genome contains two sets of cell-derived sequences, ets and myb. myb sequences are also present in avian myeloblastosis virus, which transforms myeloblasts exclusively. To determine whether the ets sequence is responsible for the erythroid specificity of E26, we analyzed the transforming activities of several viruses carrying mutations in the ets sequence constructed in vitro. The mutant viruses retained the ability to transform myeloid cells in vitro, indicating that the myb oncogene is sufficient for this viral function. However, the ets-deficient viruses did not cause an overt leukemia in chickens. The results indicate that the ets sequence is required for the induction of erythroblastosis by E26.     

An unexpected by-product obtained during the preparation of technetium(III) boronic acid adducts of dioximes. The single crystal structure of TcCl(DMG)2(BDI)BEt (DMG=dimethylglyoxime, BDI=butane-2, 3-dione imine-oxime)

An unusual Tc(III) boron-capped imine-oxime complex has been isolated from the reaction of ⁹⁹TcCl₃(CH₃CN)(PPh₃)₂, dimethyl glyoxime (DMG) and ethyl boronic acid (EtB(OH)₂). A single crystal X-ray structure analysis of this molecule ⁹⁹TcCl(DMG)₂(BDI)BEt (BDI=butane-2, 3-dione imine-oxime) shows it to be seven coordinate: TcClC₁₄H₂₅N₆O₅B, a=9.073(2), b=23.686(5), c=19.539(6) Å; β=93.77(2)°, P2₁/n, Z=8. Its structure is very similar to that of previously reported Tc(III) complexes ⁹⁹TcCl(dioxime)₃BR, except that one dioxime ligand on the molecule has been reduced to an imineoxime.