Lambda transducing phages derived from a finO- R100::λ cointegrate plasmid: Proteins encoded by the R100 replication/incompatibility region and the antibiotic resistance determinant

Abstract

Three λ transducing phages have been isolated from pEDR20, an R100:: λ cointegrate plasmid in which the λ insertion inactivated the R100 finO gene. Physical analysis of the three phages showed that the λ is inserted at kilobase coordinate 81.3 of R100. All three phages carry different amounts of R100 DNA in the left arm of λ. Each phage contains IS1b, the mer genes and the region between coordinate 81.3 and 88.6; thus, all contain the genes necessary for R100 replication. One phage, VAλ73, contains the entire r-determinant of R100 in addition to the above DNA. Five proteins coded by the region between 81.3 and 88.6 were detected. These had subunit molecular weights of 10,400; 12,200; 16,200; 19,600; and 38,300. The first was made constitutively and the other four only from a λ promoter. Other constitutive proteins were one from the cml fus region with a molecular weight of 22,400 (cml) and two from the str sul region with molecular weights of 31,500 (str?) and 30,100 (sul?). Mercuric ion induced synthesis of at least 10 proteins. Six of these were known from earlier work. The total size of the proteins which appear to derive from the mer genes exceeds by a factor of 1.5, the coding capacity of this region without overlapping genes. Some, or all of these extra proteins may be chromosomal in origin, possibly derepressed in response to mercury gene products.