[Construction of a bacterial artificial chromosome (BAC) contig encompassing the bacterial blight resistance gene Xa4 locus in rice]

The gene Xa4 confers dominantly resistance to rice bacterial blight, which has been finely mapped between RFLP markers G181 and L1044, and co-segregated with the resistance gene homologues sequence marker RS13. The three markers were used to screen a rice Bacterial Artificial Chromosome (BAC) library constructed from IRBB56, a Xa4-harborring indica variety, resulting in the detection of totally 128 positive clones. Of the 18 positive clones picked out by RS13, 4 and 6 clones were simultaneously detected by G181 and L1044, respectively. Based on their HindIII restriction patterns, 12 clones were selected out to construct a contig that spanned about 420 kb covering the Xa4 locus, which is a solid base for the isolation of Xa4 gene.

Purification and characterization of the apically secreted 80 KDa glycoprotein from Madin-Darby canine kidney (MDCK) cells

An 80 KDa glycoprotein (gp 80), known to be released predominantly from the apical surface by filter-grown Madin-Darby canine kidney cells, was purified to electrophoretic homogeneity. Purified gp 80 was found to have a disulfide-bonded dimeric structure, and appeared to exist in two molecular forms, a major (high-molecular weight) form consisting of a 46 KDa subunit and a 39 KDa subunit and a minor (low-molecular weight) form consisting of a 46 KDa subunit and a 33 KDa subunit. Upon de-glycosylation by N-glycanase treatment, the 46 KDa subunit was converted to a 25.6 KDa form, whereas both the 39 KDa and the 33 KDa subunit gave rise to a 21.1 KDa form. V8 protease mapping of deglycosylated polypeptides revealed the 39 KDa and the 33 KDa subunit to have nearly identical band patterns, which also exhibited a high degree of homology to that derived from the 46 KDa subunit. Radioimmunoassays revealed that the binding of the purified gp 80 to fibrinogen (or heparin) was dependent on both pH and divalent cations. Furthermore, binding of gp 80 to immobilized fibrinogen (or heparin) was inhibited in the presence of free fibrinogen (or heparin) added in the assay mixture.

Purification and characterization of a membrane-bound tyrosine-O-sulfate-binding protein from bovine liver

A membrane-bound 175-kDa tyrosine-O-sulfate (TyrS)-binding protein from bovine liver was purified to electrophoretic homogeneity. The purified protein exhibited an apparent molecular weight of 175,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions. Upon SDS-PAGE under nonreducing conditions, the TyrS-binding protein migrated considerably faster than the dimeric fibronectin, indicating its presence in the monomeric form and therefore the absence of a disulfide-bonded subunit structure. The purified TyrS-binding protein was found to bind concanavalin A-Sepharose and yielded a positive reaction toward periodic acid-Schiff (PAS) staining, indicating its glycoprotein nature. The purified TyrS-binding protein displayed strong binding to TyrS, but not the unmodified tyrosine, covalently bonded to Sepharose. Using a tyrosine-sulfated cholecystokinin octapeptide (CCK-8) as the ligand in a radioimmunoassay, it was found that the binding of the TyrS-binding protein was pH-dependent, being strong from pH 8.0 down through 6.5, and becoming dramatically weaker at pH below 6.0. Divalent cations, added in the assay mixture, exerted significant promoting effects on the binding in the order Mn+2 greater than Ca2+ greater than Mg2+. Western blot analysis clearly showed that the purified TyrS-binding protein was capable of forming complexes with two tyrosine-sulfated proteins, fibronectin and fibrinogen, but not two non-tyrosine-sulfated proteins, transferrin and albumin. These results provided support to a role of the TyrS-binding protein being a putative receptor for tyrosine-sulfated proteins.

Identification of complexes between the tyrosine-O-sulphate-binding protein and tyrosine-sulphated proteins in bovine liver membrane lysates

Rabbit antiserum against electrophoretically purified bovine liver tyrosine-O-sulphate (TyrS)-binding protein was prepared. Affinity-purified antibodies from the antiserum were found to be capable of immunoprecipitating the TyrS-binding protein from the sodium choleate extract of a bovine liver microsomal membrane fraction. Using purified specific antibodies as the probe, Western blot analysis for the presence of TyrS-binding protein/tyrosine-sulphated protein complexes in bovine liver membrane lysates was performed. It was found that the TyrS-binding protein co-precipitated with three tyrosine-sulphated proteins (fibronectin, fibrinogen and complement C4) immunoprecipitated by their respective antibodies. In contrast, for the two non-tyrosine-sulphated proteins (haptoglobin and transferrin) tested, co-precipitation of the TyrS-binding protein was not observed. On employing an affinity gel fractionation technique, it was shown that partially purified TyrS-binding protein exhibited binding affinity towards Sepharose gels covalently bonded to fibronectin or fibrinogen, but not towards Sepharose gels bonded to albumin or transferrin. These results indicate that the TyrS-binding protein formed complexes with tyrosine-sulphated proteins both in vivo and in vitro, and thus provide support for the putative role of the former being the receptor of the latter.

The active site of the thrombin-thrombomodulin complex. A fluorescence energy transfer measurement of its distance above the membrane surface

The location of the active site of the membrane-bound anticoagulant complex of thrombin and thrombomodulin has been determined relative to the membrane surface using fluorescence energy transfer. Thrombin was reacted with 5-(dimethylamino)-1-naphthalenesulfonylglutamylglycylarginyl chloromethyl ketone (DEGR-CK) to yield DEGR-thrombin, an analogue of thrombin with a fluorescent dye covalently attached to its active site. When DEGR-thrombin was titrated with thrombomodulin that had been reconstituted into phospholipid vesicles containing octadecylrhodamine, singlet-singlet energy transfer was observed between the donor dyes, each in an active site of a DEGR-thrombin bound to thrombomodulin, and the acceptor dyes at the outer surface of the phospholipid bilayer. The extent of energy transfer reached a maximum when DEGR-thrombin and thrombomodulin were equimolar in the sample, as expected for the formation of a 1:1 complex between thrombin and thrombomodulin. This energy transfer was dependent upon the binding of DEGR-thrombin to thrombomodulin because no energy transfer was observed with vesicles that lacked thrombomodulin, and the extent of energy transfer was reduced greatly by the addition of excess unmodified nonfluorescent thrombin to compete with DEGR-thrombin for binding to the thrombomodulin. From the dependence of the energy transfer upon the acceptor density and assuming kappa 2 = 2/3, the distance of closest approach between a dye in the active site of the thrombin-thrombomodulin complex and a dye at the membrane surface was determined to average 66 A (65 +/- 3 A for phosphatidylcholine vesicles without and 67 +/- 5 A for those with 20% phosphatidylserine). This distance was also insensitive to the presence or absence of Ca2+. These direct measurements indicate that the active site of the membrane-bound thrombin-thrombomodulin complex is located far above the phospholipid surface, that the peptide bond cleaved during the activation of protein C is situated about 66 A above the membrane, that the thrombin binding site on thrombomodulin is positioned more than 45 A above the membrane, ant that thrombin, with a diameter near 40 A, is not positioned alongside thrombomodulin near the membrane to form the thrombin-thrombomodulin complex but is instead bound "on top" of thrombomodulin.