New locus (ttr) in Escherichia coli K-12 affecting sensitivity to bacteriophage T2 and growth on oleate as the sole carbon source.

The nature of resistance to phage T2 in Escherichia coli K-12 was investigated by analyzing a known phage T2-resistant mutant and by isolating new T2-resistant mutants. It was found that mutational alterations at two loci, ompF (encoding the outer membrane protein OmpF) and ttr (T-two resistance), are needed to give full resistance to phage T2. A ttr::Tn10 mutation was isolated and was mapped between aroC and dsdA, where the fadL gene (required for long-chain fatty acid transport) is located. The receptor affected by ttr was the major receptor used by phage T2 and was located in the outer membrane. Phage T2 was thus able to use two outer membrane proteins as receptors. All strains having a ttr::Tn10 allele and most of the independently isolated phage T2-resistant mutants were unable to grow on oleate as the sole carbon and energy source, i.e., they had the phenotype of fadL mutants. The gene fadL is known to encode an inner membrane protein. The most likely explanation is that fadL and ttr are in an operon and that ttr encodes an outer membrane protein which functions in translocating long-chain fatty acids across the outer membrane and also as a receptor for phage T2.