GENE-19 OF PLASMID-R1 IS REQUIRED FOR BOTH EFFICIENT CONJUGATIVE DNA TRANSFER AND BACTERIOPHAGE-R17 INFECTION

F-like plasmids require a number of genes for conjugation, including t ra operon genes and genes traM and traJ which lie outside the tra oper on. We now establish that a gene in the ''leading region,'' gene 19, p rovides an important function during conjugation and RNA phage infecti on. Mutational inactivation of gene 19 on plasmid R1-16 by introductio n of two nonpolar stop codons results in a 10-fold decrease in the con jugation frequency. Furthermore, infection studies with the male-speci fic bacteriophage R17 revealed that the phage is not able to form clea r plaques in Escherichia coli tells carrying an R1-16 plasmid with the defective copy of gene 19. The total number of cells infected by phag e R17 is reduced by a factor of 10. Both the conjugation- and infectio n-attenuated phenotypes caused by the defective gene 19 can be complem ented in trans by introducing gene 19 alleles encoding the wild-type p rotein. Restoration of the normal phenotypes is also possible by intro duction of the pilT gene encoded by the unrelated IncI plasmid R64. Ou r functional studies and similarities of protein 19 to proteins encode d by other DNA transfer systems, as well as the presence of a conserve d motif in all of these proteins (indicative for a putative muramidase activity) suggest that protein 19 of plasmid R1 facilitates the passa ge of DNA during conjugation and entry of RNA during phage infection.