Since the discovery of bacterial homologues to tubul~n, actin and intermediate fila~ents the presence of a cytoskeleton can no longer be viewed as a fundamental distinction between the eukaryotic and prokaryotic lineages. How bacteria utilize these cytoskeletal proteins in the cell remains an important question. This thesis describes the characterisation of the first non polar mutant of mreB, a bacterial actin homologue suggested to have a role in chromosome segregation. mreB was found to be essential and the discovery that high levels ofMg2+ rescue an mreB mutant has led to a reassessment of its role in Bacillus subtiUs. In the absence of gross morphological defects, no obvious role for MreB in chromosome segregation was observed. Instead the main role ofMreB appears to be in control ofcell width. Sub-cellular localization of several key proteins involved in WTA synthesis and export, revealed that they are present both at sites of cell division and in a helical like pattern over the lateral cell wall. Bacterial two-hybrid interactions suggested that WTA biosynthetic proteins form a multi-enzyme complex, which might be as~ociated with the bacterial cytoskeleton either directly, through MreB, or indirectly through interactions with MreC and MreD. Pairwise combinations of CFP and YFP fusions to the MreB isoforms: MreB, Mbl and MreBH showed that all three proteins colocalized and might be present in a single h~lical protofilament, located at the cell periphery. Some functional redundancy was also seen between the MreB isoforms suggesting that they have partially overlapping functions. These results, taken together with other findings, support a revised model in which the overall strategy by which B. subtilis achieves controlled extension and accurate maintenance of its rod shape may be based on a helical pattern of insertion of PO and WTA synthesizing and PO hydrolysing activities, governed by the MreB isoforms.