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Endoglucanase CenA of Cellulomonas fimi comprises an N-terminal cellulose-binding domain and a C-terminal catalytic domain joined together by a sequence of 23 proline and threonine residues (the Pro-Thr box). The domains function independently when separated by proteolysis. TnphoA has been used to generate cenA′-′phoA fusions. CenA′-′PhoA fusion polypeptides which contain the entire cellulose-binding domain of CenA bind to cellulose, allowing their purification from periplasmic extracts in a single, facile step. This result has implications for purification or immobilisation of chimeric proteins on a cheap cellulose matrix.

Several groups have attempted to identify the EGF receptor by a variety of biochemical techniques. Das et al. [l] identified the EGF receptor on 3T3 cells as a radioactive band of M, = 190 000 by photoaffmity labeling with a ‘251-EGF probe; Hock et al. [2] identified the EGF receptor in human placenta as a doublet of 160 000 and 180 000 M, by covalent cross-linking to ‘251-labeled EGF. The EGF receptor on A-43 1 cells was identified [3] as a radioactive band of M, 175 000 by ‘direct labeling’, which is accomplished by incubation of cells with 1251-EGF. Cohen and coworkers [4] have partially purified the EGF receptor of A-43 1 cells by affinity chromatography and analyzed the denatured proteins of such preparations by SDS-polyacrylamide gel electrophoresis. They found numerous protein bands in the affinity-purified preparations and suggested that a major protein band of M, 150 000 is the receptor for EGF in A-431 cells. More recently, Hunter and Cooper [S] isolated the EGF receptor from 32P-labeled A-43 1 cells by immunoprecipitation with an antiserum raised against crude plasma membrane from A-431 cells. They have estimated the M, of the EGF receptor present in the immunoprecipitates from A-43 1 cells as 155 000. The interaction of EGF with its membrane receptor, present in both crude plasma membranes from A-431 cells and in affinity-purified prepara

Plasminogen activation occurs through conversion of plasminogen to plasmin by plasminogen activators. In adult mammals, liver has been the only known site for plasminogen synthesis. Seminiferous tubules secrete plasminogen activator, but are behind a barrier that excludes the entrance of many macromolecules to this tissue. Therefore, it became of interest to study the existence of plasminogen in this system. After metabolic labeling, a 90 kDa lysine-binding polypeptide was found. This protein could be immunoblotted by anti-plasminogen antibody, and was shown to possess urokinase-dependent proteolytic activity. The findings suggest that plasminogen is synthesized by seminiferous tubules. We propose that local plasminogen synthesis may occur in tissues which are separated by specific anatomical barriers.

The affinity of epidermolytic toxin from Staphylococcus aureus for proteins from the target tissue has been tested by a Western blotting procedure. Particular proteins in a l M phosphate extract of epidermis reacted on nitrocellulose blots with a probe prepared by the conjugation of toxin with peroxidase. Protein extracted into 50 mM Tris-HCl did not react. The probe detected profilaggrin, filaggrin and a smaller unidentified polypeptide. It is suggested that the interaction is relevant to the mode of action of the toxin.