MULTIMERS OF THE PRECURSOR OF A TYPE-IV PILIN-LIKE COMPONENT OF THE GENERAL SECRETORY PATHWAY ARE UNRELATED TO PILI

Both the mature and precursor forms of PulG, a type IV pilin-like comp onent of the general secretory pathway of Klebsiella oxytoca, can be c hemically cross-linked into multimers similar to those obtained by cro ss-linking the components of type IV pill. To explore the possibility that the PulG precursor could form a pilus-like structure, the PulG se quence was altered in a variety of ways, including (i) replacement of the characteristic hydrophobic region, which is required for the assem bly of type IV pilins by the MalE signal peptide, or (ii) fusion of be ta-lactamase (beta laM) to the C-terminus. Neither of these changes af fected multimerization. PulG precursor could be post-translationally p rocessed by prepilin peptidase (PulO), indicating that the N-terminus of prePulG remains on the cytoplasmic side of the cytoplasmic membrane where it is accessible to the catalytic site of this enzyme. Finally, precursor and mature forms of PulG could be efficiently cross-linked in a mixed dimer, indicating that at least a subpopulation of the two forms of the protein are probably located in clusters in the cytoplasm ic membrane. These results provide further evidence that the crosslink ed multimers of the precursor form of PulG are unrelated to type IV pi lus-like structures. It is still unclear whether a subpopulation of pr ocessed PulG can be assembled into a rudimentary pilus-like structure.