We have cloned into Escherichia coli the genes for 38 type-II bacterial modification methyltransferases. The clones were isolated by selecting in vitro for protectively modified recombinants. Most of the clones modify their DNA fully but a substantial number modify only partially. In approximately one-half of the clones, the genes for the corresponding endonucleases are also present. Some of these clones restrict infecting phages and others do not. Clones carrying endonuclease genes but lacking methyltransferase genes have been found, in several instances, to be viable.

SYNOPSIS. Light-and electronmicroscopic observations on Dientamoeba fTagilis strain A (Bi) 1 dealing primarily with the binucleate (arrested telophase ) stages, predominant in all populations, revealed the microtubular nature of the extranuclear spindle which extends between the 2 polar complexes each adjacent to one of the nuclei. The spindle microtubules originate in paired, nonperiodic structures apparentIy homologous to the "atractophores" described from hypermastigotes. To the external surface of the atractophores are applied periodic elements, which extend laterally as the parabasal filaments. Extensive Golgi complexes overlie the filaments, these structures corresponding to the components of the parabasal apparatus known from trichomonads and hypermastigotes. The 2-layered structures, consisting of the atractophores and periodic layers, together with the proximal parts of the Golgi complex and the spindle microtubules constitute the polar complex. No kinetosomeor centriole-like organelles have been found in the polar complexes or elsewhere in the organism. The extranuclear spindle is composed of 2 microtubule bundles, each with -30-40 mirrotubules. One of the bundles always appears at some distance from the nucleus; the other is juxtanuclear and is seen often to course within a groove of the nuclear envelope. A M e d . Hyg. 56, 535-7. 97. -1972. Structure and movement of Entamoeba. Ann. Trop. M e d . Parasit. 66, 329-34. 245-52. 77, 185-205.

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This ultrastructural study describes the origin of Woronin bodies from microbodies in intercellular hyphae of the plant pathogen Cymadothea trifolii. In this fungus the development of Woronin bodies begins with the appearance of electron-dense material within the microbody. Subsequently, this material is confined to a developing evagination of the delimiting microbody membrane. Eventually the protrusion containing the electron-dense material is released as a Woronin body via an exocytotic mechanism. Woronin bodies are frequently found near septal pores and probably contribute to the formation of septal pore plugs.