Elizabeth H. Szybalski

A Comprehensive Molecular Map of Bacteriophage LAMBDA

Physical and genetic mapping of deletion mutations has been correlated with the available molecular sizes of the lambda gene products and the DNA base sequence to construct a comprehensive molecular map of the phage lambda genome. The physical length of the DNA making up the left arm from the cos site through gene J is not sufficient to account in a nonoverlapping manner for all the proteins of the sizes reported to be coded, especially in the Nu1--C region. In the right arm all the coding capacity has not been accounted for, and it appears to be oversaturated only in the gam-ral region. The positions of several IS and Tn elements, and of restriction endonuclease cleavage sites are specified.

Physical mapping of the att-N region of coliphage lambda: Apparent oversaturation of coding capacity in the gam-ral segment

Summary Employing a series of λbio deletion mutants, the genes int, xis, Ea22, exo, bet, gam, kil, cIII, Ea10, ral and N and their known protein products have been ordered in respect to the physical map of λ, as constructed by electron microscopy of heteroduplexes between the λbios and λattR-attLs (λatt2imm21 or λatt2imm434). Throughout most of this region the coding capacity is about saturated, as based on the known sizes of the λ proteins and the positions of the genetic and physical endpoints of the bio deletions. One baffling exception is the gam-kil-cIII segment, which cannot accommodate all three of the corresponding proteins. The second exception is the region between genes ral and N, which could code for a protein about 25,000 daltons, but for which no proteins have been identified. The space available for gene N suggests that its product must be a protein of no more than 15,000 daltons in size. Physical mapping of the bio386 deletion has established that proteins Ea42(int), Ea32(xis ?) and Ea22 are encoded in that order.

A physical map of the Escherichia coli bio operon

The endpoints of the Escherichia coli bio DNA insertions in 24 lambda bio transducing phage were mapped electron micrographically in heteroduplexes of the type lambda bio/lambda att2, which permit simultaneous measurement of the lambda deletion and bio insertion endpoints. A physical map of the bio operon was constructed and correlated with the genetic map, the molecular sizes of the bio gene products, and the restriction map. The order att lambda-bioA-pBopA-bioBFCD-uvrB was confirmed. The maximum size of the bio operon was estimated at 5.5 kb, and the locus was found to be fully saturated with genes. There appears to be little space between the bioA gene and att lambda, while bioD mapped within 0.7 kb from uvrB. The size of the uvrB locus was estimated not to exceed 2.6 kb.