Overlapping of the coding regions for alpha and gamma components of penicillin-binding protein 1 b in Escherichia coli

Abstract

The mode of biosynthesis of penicillin-binding protein(PBP)-1b in Escherichia coli was investigated by use of the plasmid carrying the ponB(PBP-1b) gene region. Analyses of the products synthesized in minicells and in vitro showed that PBP-1b was synthesized as two molecular species corresponding to the alpha and gamma components of PBP-1b. The coding regions for the alpha and gamma components were located within the ca. 3.7 kb MluI-HincII fragment and transcribed in the direction from the HincII to the MluI site. The capacity for producing the alpha component was abolished by a deletion extending to the MluI site ca. 0.7 kb inward from the HincII end of the ca. 3.7 kb fragment; the remaining 3.0 kb region with the MluI site at both ends directed the production of the gamma component alone. The production of the gamma component was enough to correct all the known defects caused by a ponB mutation. In addition to these results, the analyses for cross-reacting materials produced in correspondence to the various deletions indicated that the coding regions for the alpha and gamma components overlapped and that the N-terminal portion was responsible for the difference between the two components. The distal region about 0.7 kb long inward from the MluI end of the MluI-HincII fragment was dispensable for producing the functional PBP-1b, although the PBP-1b produced was curtailed. By a larger distal deletion reaching almost to the middle of the MluI-HincII fragment, the polypeptide produced for PBP-1b lost the ability to bind penicillin and still retained a low but significant activity for glycan synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)