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The molecular origin of lambda prophage mRNA.

Lambda-specific RNA extracted from lysogenic bacteria hybridizes specifically with fragments of lambda DNA containing 43 per cent GC (guanine plus cytosine). Therefore genes known to function in the prophage state (c(I) and rex) lie 0.38 +/- 0.08 fractional molecular length from the right end of the lambda DNA molecule, according to the compositional map of Skalka, Burgi, and Hershey.

Centrifugation, Density Gradient↗

Simian virus 40 integration site in an adenovirus 7-simian virus 40 hybrid DNA molecule.

The E46(+) strain of Adenovirus 7 is a mixed-virus population containing defective Adenoviurs 7-SV40 hybrid particles and helper, nonhybrid Adenovirus 7 particles. We have applied electron microscopic mapping techniques to obtain a physical map of the genome of the hybrid particles present in E46(+)PL1, a substrain of E46(+) derived from a single two-hit plaque. DNA molecules extracted from purified E46(+)Pl1 virions were found to be linear duplexes, with a mean lenght of 10.9 mum. When these molecules were denatured and renatured, a unique heteroduplex was formed that presumably derived one of its strands from an Adenovirus 7-SV40 hybrid molecule and the other from a nonhybrid Adenovirus 7 molecule. This heteroduplex was double-stranded, except for a short region near one end where the two strands were not paired. On the basis of measurements of the lengths of the single-and double-stranded regions in the heteroduplex, the structure of the Adenovirus 7-SV40 hybrid genome can be reconstructed as follows: The hybrid genome contains 16% less Adenovirus 7 DNA than the nonhybrid Adenovirus 7 genome. This deletion consists of the segment of DNA that maps between 0.05 and 0.21 molecular lenghts in the nonhybrid Adenovirus 7 DNA molecule. The deleted DNA has been partially replaced by an amount of heterologous DNA equivalent to 75% of the complete SV40 genome. A model for the generation of the hybrid genome is presented.

Adenoviridae↗

Evidence for mitotic recombination in the cellular slime mold Dictyostelium discoideum.

A mutant resistant to methanol was isolated and the mutation was shown to be located on the same linkage group with two other previously identified markers, white spore color and temperature sensitivity. In the course of analyzing methanol-resistant haploid segregants, four classes of methanol-resistant diploids were found. It is proposed that these represent mitotic recombinants, and a map of the chromosome is suggested. Segregation analysis of the diploids shows the genotypes of the diploids to be in perfect agreement with the mitotic recombination model.

Chromosome Mapping↗

Agents of mycobacterial variations.

Mycobacterial variations are determined by physicochemical agents or by genetic transfers. The pioneer work done on the study of the effects of light, radiation, heat, nutritional factors, and drugs is reviewed. Technical and conceptual problems arise in the study of genetic transfer by means of conjugation and transformation in mycobacteria. Transduction and lysogenic conversion are shown to be responsible for important changes in bacterial and colony morphology, enzymatic activities, bacteriophage and drug resistance. Results of recent experiments with different strains of bacille Calmette-Guérin (BCG) suggest a relationship between phage conversion and the degree of immunogenic potential.

Conjugation, Genetic↗