Analysis of OmpC-beta-lactamase hybrid proteins: OmpC appears not to contain discrete localization signals

Fusions to the beta-lactamase (bla) gene were employed to analyze the presence of localization information in the mature part of OmpC, a major pore-forming outer membrane protein in Escherichia coli K-12. Six translational ompC-bla gene fusions were constructed, the shortest of them containing only part of the ompC signal sequence and the largest approximately 90% of the sequence encoding mature OmpC protein. Export of the hybrid proteins to a non-cytoplasmic location was a prerequisite for ampicillin resistance. Localization of the hybrid proteins by cell fractionation and solid phase iodination of whole cells suggested that the exported hybrid proteins possibly interacted with the outer membrane in vivo. No specific sequence of the mature OmpC protein, however, was found to promote this interaction.