The binding of the essential cell division protein FtsN of Escherichia coli to the murein (peptidoglycan) sacculus was studied. Soluble truncated variants of FtsN, including the complete periplasmic part of the protein as well as a variant containing only the C-terminal 77 amino acids, did bind to purified murein sacculi isolated from wild-type cells. FtsN variants lacking this C-terminal region showed reduced or no binding to murein. Binding of FtsN was severely reduced when tested against sacculi isolated either from filamentous cells with blocked cell division or from chain-forming cells of a triple amidase mutant. Binding experiments with radioactively labeled murein digestion products revealed that the longer murein glycan strands (>25 disaccharide units) showed a specific affinity to FtsN, but neither muropeptides, peptides, nor short glycan fragments bound to FtsN. In vivo FtsN could be cross-linked to murein with the soluble disulfide bridge containing cross-linker DTSSP. Less FtsN, but similar amounts of OmpA, was cross-linked to murein of filamentous or of chain-forming cells compared to levels in wild-type cells. Expression of truncated FtsN variants in cells depleted in full-length FtsN revealed that the presence of the C-terminal murein-binding domain was not required for cell division under laboratory conditions. FtsN was present in 3,000 to 6,000 copies per cell in exponentially growing wild-type E. coli MC1061. We discuss the possibilities that the binding of FtsN to murein during cell division might either stabilize the septal region or might have a function unrelated to cell division.Division of the rod-shaped bacterium Escherichia coli includes the formation of two new polar caps of the daughter cells. Division is facilitated by the so-called divisome, a ring structure at the tip of the inward-growing septum (12, 44). About twelve known essential cell division proteins (Fts proteins) were shown to localize at this site (47). Probably the best characterized Fts protein is FtsZ, a homolog of eukaryotic tubulin, which is the first known protein that localizes at the division site and which forms a ring-like polymeric structure (5,16,39,40,52). The localization of all other cell division proteins depends on the presence of FtsZ. It is assumed that FtsZ may provide not only the platform for the assembly of the other components of the divisome but also the force for constriction by its ability to utilize energy from GTP hydrolysis. The FtsZ ring is stabilized by and maybe connected to the membrane via ZipA (21, 29, 30, 38) and FtsA, which has an actin-like fold (2,42,43,49,55,59). The assembly of the divisome then continues with the sequential localization of the predicted ABC transporter FtsEX (54), followed by the membrane proteins FtsK (3), FtsQ (7, 9), FtsL (15,23,27), YgbQ (now termed FtsB) (8), and FtsW (6, 46) at the FtsZ-FtsAZipA ring. After FtsW, the monofunctional murein transpeptidase penicillin-binding protein 3 (PBP3; also named FtsI) localizes at the site of division (48, 61, 62), foll...

The rapid degradation of ribonucleic acids (RNA) by ubiquitous ribonucleases limits the efficacy of new therapies based on RNA molecules. Therefore, our aim was to characterize the natural ribonuclease activities on the skin and in blood plasma i.e. at sites where many drugs in development are applied. On the skin surfaces of Homo sapiens and Mus musculus we observed dominant pyrimidine-specific ribonuclease activity. This activity is not prevented by a cap structure at the 5'-end of messenger RNA (mRNA) and is not primarily of a 5'-or 3'-exonuclease type. Moreover, the ribonuclease activity on the skin or in blood plasma is not inhibited by chemical modifications introduced at the 2'OH group of cytidine or uridine residues. It is, however, inhibited by the ribonuclease inhibitor RNasin ® although not by the ribonuclease inhibitor SUPERase· In™. The application of our findings in the field of medical science may result in an improved efficiency of RNA-based therapies that are currently in development.