This project will attempt to elucidate the molecular basis for natural variation in resistance to phagocytosis by virulent group A Streptococci. Employing genetic and biochemical techniques the role of bacteriophage and chromosomal genes in the regulation of M protein synthesis will be investigated. Experimental data will further evaluate preliminary evidence that lysogenic conversion imparts resistance to phagocytosis. Comparison of restriction endonuclease maps of Bacteriophage DNA will extend our understanding of interactions between the virus and bacteria which result in resistance to phagocytosis.