Biomedical subjects
Publications and source records attributed to M Z Humayun.
By in vitro methods, we have deleted 80 nucleotides from a preselected site in the coding sequence of gene G of bacteriophage phiX174. This mutant (Gdelta/FS ZH1) also carries a--2 frameshift. The mutation is lethal, but mutant virus can be stably maintained on host strains bearing plasmids carrying phiX gene G.
In order to study the mutagenic effects of site-specific, covalent modifications of biologically active DNA, we need host cells that are permissive for any type of mutation that might be produced in vivo from the modified DNA. Specifically, we require a general, in vivo complementation system for the bacteriophage phiX174 gene G, an essential gene that we have chosen for our initial studies of chemical mutagenesis. Toward this end, we have constructed a plasmid (pphiXG) that carries a functional copy of phiX174 gene G. Three different bacterial strains that are nonpermissive for am9, a gene G amber mutant, have been transformed with pphiXG. The transformants are now permissive for this gene G mutant, but not for the gene A or E mutants that have been tested. This paper describes the construction and the biochemical characterization of this plasmid, pphiXG, and describes some of the biological properties exhibited by the pphiXG-bearing strains.
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Antibodies were raised in rabbits against the bovine serum albumin conjugate of dpApT. Analysis by double diffusion in agar gel and quantitative precipitation test showed the presence of antibodies specific to the hapten in the antisera. Quantitative data on the specificity of the antibodies were obtained by studying the inhibition of the binding of 3H-dpApT to the antisera by various nonradioactive mono- and oligonucleotides, using a nitrocellulose membrane binding assay. The antibodies were found to be highly specific for the dinucleotide sequence dpApT. The antibodies were able to bind to synthetic oligonucleotides containing the sequence dpApT and to denatured calf thymus DNA.
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