YPSB, A NEW DIVISION PROTEIN OF BACILLUS SUBTILIS LIKELY INVOLVED IN SEPTAL PEPTIDOGLYCAN SYNTHESIS.

José Roberto Tavares (USP); Robson Francisco Souza (USP); Guilherme Louzada Silva Meira (USP); Frederico José Gueiros Filho (USP)

The main form of reproduction in prokaryotes is binary division. In Bacillus subtilis this process is executed by the divisome, a macromolecular machine containing at least sixteen proteins which assembles at the site of division. We have used bioinformatics to identify a new division protein of B. subtilis, YpsB. Sequence comparison and phylogenetic analysis demonstrated that YpsB is a paralog of the division-site selection protein DivIVA. We used GFP microscopy to determine the subcellular localization of YpsB. This revealed that YpsB is a component of the divisome, and that, similarly to DivIVA, recruitment of YpsB to the divisome requires the late divisome proteins and occurs significantly after Z-ring formation. However, we found that the assembly of YpsB occurs independently of MinCD and DivIVA proteins. Deletion analyses suggest that the N-terminus of YpsB is involved in its targeting to the divisome. YpsB is not essential for septum formation and does not play a role in septum positioning. Nevertheless, a ypsB deletion has a synthetic lethal effect when combined with a deletion of the gene for FtsA, another division protein whose role is to help assemble the FtsZ ring. Fluorescence microscopy of the ypsB^- ftsA^- double-mutant showed filamentation, fragile membrane and cell lyses, suggesting that YpsB is involved in the final steps of division, possibly affecting peptidoglycan synthesis.