PENICILLIN-BINDING PROTEINS ARE REGULATED BY RPOS DURING TRANSITIONS IN GROWTH STATES OF ESCHERICHIA-COLI

Attention has been recently focused on the role of the rpoS (formerly katF) gene product as a regulator during the transition from the expon ential growth phase to the stationary phase as well as during nutritio nal starvation. It has been demonstrated that RpoS is an alternate sig ma factor which would bind to promoters of genes induced at these time s. It was previously noted that rpoS mutants do not undergo a transiti on to short rods during entry into the stationary phase. Because of th eir well-established role in morphogenesis, we investigated the status of the penicillin-binding proteins (PBPs) in Escherichia coli wild-ty pe and isogenic rpoS mutants. Samples from cultures of E. coli ZK126 a nd ZK1000 (rpoS=kan) were taken in the midlogarithmic, early stationar y, and late (24 h) stationary phases. The increase in PBP 6 seen upon entry of the wild-type strain into the stationary phase was not observ ed with the rpoS=kan cells, even after 24 h. There was also a marked d ecrease of PBP 3 in wild-type stationary-phase cells; PBP 3 has a know n influence on morphogenesis. This decrease in PBP 3 was found to be m arkedly affected by the disruption of rpoS. Similar observations were made after prolonged starvation of the two strains for either glucose or a required amino acid. Inasmuch as PBPs are involved in peptidoglyc an synthesis, we also examined two properties of peptidoglycan, autoly sis and cross-linkage, that might be altered by the PBP differences. H owever,neither of these properties, which are known to undergo changes in the stationary phase, appeared to be influenced by the status of R poS.