9417052 Vijayakumar This project deaa novel class of transposable elements capable of intracellular as well as intercellular transposition. Besides being the major vehicles for the horizontal spread of multiple antibiotic resistance among streptococci, they also have been shown to transfer between Gram-positive and Gram-negative bacteria. Experimental observations have shown that there are at least two distinct classes of streptococcal conjugative transposons, one typified by Tn916 and the other class of much larger elements typified by Tn5252 originally discovered in pneumococcus. In nature, these two independent classes of conjugative transposons are often found physically associated. At present, the molecular basis for this relationship is unclear. While considerable efforts are being spent investigating the smaller elements, little is known about the larger ones. Studies relating to the physical structure of Tn5252 revealed at least six potemtial genes whose products could be related to its transposition functions. This project aims to establish the structure-function relationships of two of these genes and their products, a repressor-like and a DNA relaxase-like proteins and to further localize other genes involved in the conjugal transposition of this element. The experiment being performed employ a variety of genetic and biochemical techniques to mutagenize the loci involved and to characterize their protein products. The lack of plasmids within pneumococcus, a naturally highly transformable bacterium, is an enigma that needs to be addressed. Heterologous alaments such as Tn5252 appear to functionally replace plasmids in this organism. Tn5252 provides a model system to study unusual genomic rearrangements predicted to occur and play a role in the evolution of heterogeneity in this species. %%% The investigation could enlarge our understanding of the origin and autoaccumulation of mobile elements some of which may carry antibiotic resistance determinants. Moreover, these st udies may enable the construction of a smaller version of the element to be used as a genetic tool to introduce heterologous genes of interest into nontransformable streptococci. Such a system has advantages such as stability and the potential to add a series of genes to the same chromosome. ***
