SUMMARYBacteriophage 2 particles were rendered osmotically fragile by incubation, spread over hypophase and examined by electron microscopy. When water was used as hypophase, condensed structures were released from the phage heads and treatment of these with cytochrome c or several alternative proteins resulted in the release of free, relaxed DNA. Phage were pretreated with nitrogen mustard, a bifunctional alkylating agent; when the condensed structures from such phage particles were treated with protein, DNA was released in small supercoiled domains. This confirmed a previous finding that bacteriophage DNA has a supercoiled topology and suggests that the winding pattern of DNA in the phage might involve small domains of coiled DNA analogous to nucleosomes. Such a conformation could be consistent with other studies on the arrangement of DNA in phage heads if the domains have parallel axes.
Chloramphenicol-resistant Myxococcus virescens were obtained by infecting myxococci with Escherichia coli specialized transducing phage PI CM. The drug-resistant myxococci were phenotypically unstable. They contained more than one type of plasmid; these plasmids were not found in the parent strain. Chloramphenicol-resistant E. coli were obtained by transformation with either a fraction of myxococcal DNA containing the plasmids or with PI CM prophage DNA. These transformants contained plasmids. Escherichia coli transformed by DNA from the myxococci contained both PlCM and myxococcal genes. Individual transformant clones differed in the genetic make-up of their plasmids. Among the myxococcal genes expressed in these plasmid-harbouring E. coli strains were a capacity for self-transmissibility and a pattern of phage sensitivity characteristic of R factor incompatibility group W. Escherichia coli transformed with P1 CM prophage contained incomplete P1 CM genomes ; none of the chloramphenicol-resistant transformants produced P1 CM phage particles. The significance of these findings for an understanding of mechanisms for the generation of R factors is discussed.
The patterns of H3‐thymidine labelling in the salivary gland chromosomes of Drosophila melanogaster were studied after alkali‐urea treatment. Four essentially different labelling patterns were found: sparse labelling mainly or only in the central axis; spot labelling with almost continuous label in the axis and around it; labelling of whole chromosomes; spot labelling without appreciable label of the central axis. The possible chronological order for these patterns was suggested on the basis of earlier results. The labelling patterns were also interpreted according to the loop model of the lampbrush stage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.