Carl A. Schnaitman1, Deborah H. Smith1, Montserrat Forn de Salsas1
1Department of Microbiology, The University of Virginia, Charlottesville, Virginia 22901.
Tóm tắt
Under most conditions of growth, the most abundant protein in the outer membrane of most strains of
Escherichia coli
is a protein designated as “protein 1” or “matrix protein”. In
E. coli
B, this protein has been shown to be a single polypeptide with a molecular mass of 36,500 and it may account for more than 50% of the total outer membrane protein.
E. coli
K-12 contains a very similar, although probably not identical, species of protein 1. Some pathogenic
E. coli
strains contain very little protein 1 and, in its place, make a protein designated as protein 2 which migrates faster on alkaline polyacrylamide gels containing sodium dodecyl sulfate and which gives a different spectrum of CNBr peptides. An
E. coli
K-12 strain which had been mated with a pathogenic strain was found to produce protein 2, and a temperate bacteriophage was isolated from this K-12 strain after induction with UV light. This phage, designated as PA-2, is similar in morphology and several other properties to phage lambda. When strains of
E. coli
K-12 are lysogenized by phage PA-2, they produce protein 2 and very little protein 1. Adsorption to lysogenic strains grown under conditions where they produce little protein 1 and primarily protein 2 is greatly reduced as compared to non-lysogenic strains which produce only protein 1. However, when cultures are grown under conditions of catabolite repression, protein 2 is reduced and protein 1 is increased, and lysogenic and non-lysogenic cultures grown under these conditions exhibit the same rate of adsorption. Phage PA-2 does not adsorb to
E. coli
B, which appears to have a slightly different protein 1 from K-12. These results suggest that protein 1 is the receptor for PA-2, and that protein 2 is made to reduce the superinfection of lysogens.
