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Transformation of a rat thyroid epithelial cell line (FRTL5-C12) with Kirsten and Harvey murine sarcoma viruses (carrying the ras oncogenes) results in elevated levels of three perchloric acid-soluble nuclear phosphoproteins. These three proteins are also induced to high levels in the PC-C13 thyroid epithelial cell line when transformed by the myeloproliferative sarcoma virus (carrying the v-mos oncogene) and when transformed by transfection with the c-myc proto-oncogene followed by infection with the polyoma leukaemia virus (PyMuLV) carry the polyoma middle T antigen gene. Neither c-myc or PyMuLV alone induced high levels of the three nuclear proteins. Untransformed

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The transmissible nature of the genetic factor in Escherichia coli, which controls a-haemolysin production, was recognized by Smith & Halls (1967). The element responsible was termed Hly. The f i f character of Hly factor was described at the same time. Goebel & Schrempf (1971) demonstrated the presence in the cytoplasm of a haemolytic E. coli strain of a covalently-closed circular DNA molecule with a contour length of 29.5 ? 0.5 pm, which was transferred to non-haemolytic strains together with the haemolytic character. Therefore this DNA species represents the Hly factor. However, Hly factor was not taken into account by Hedges & Datta (1972), who classified the F-like plasmids into four compatibility groups. A further group of F-like plasmids was subsequently added by Naomi Datta in 1974 (personal communication), Folac being the prototype of it (Falkow & Baron, 1962). In the present paper we show that Hly factor determines the production of F-type pili and that it is compatible with F-like plasmids of all the five groups previously described. Escherichiu coli strain ~2 1 2 carrying Hly factor was received from H. Williams Smith. Escherichia coli strains ~5 3 and c600, carrying many known plasmids, were provided by Naomi Datta. R7, R89 and R120, three F-like R factors recently identified in Triest, were also used. Crosses were carried out by mixing equal numbers (about 2 x 107/ml) of donor and recipient cells in nutrient broth, which was subsequently incubated overnight at 37 "C. Colonies were then counted on nutrient or blood agar containing, if required, appropriated amounts of different antibiotics to define the number of donor, recipient and recombinant cells. Colonies producing colicin were identified by standard techniques. To test for the compatibility of plasmids, recombinant clones were purified on nonselective medium and tested by replica plating for the presence of each plasmid. The fif character of Hly factor was confirmed in our study. Moreover, we could show that E. coli strains carrying the Hly factor allowed a small but definite increase in the titre of MS2 phage (Davis, Strauss & Sinsheimer, 1961). This demonstrates that Hly controls the synthesis of F-pili. Being not perfectly clear from the data reported by Smith & Linggood (1970) and Smith & Heller (1973) whether Hly is self-transmissible or mobilized by the F factor, we tested different strains of E. coli K I 2 F-, which had acquired the Hly factor from E. coli strain ~2 1 2 , for sensitivity to the female-specific phages T7 and $2 (Makela, Makela & Soikkeli, 1964; Cuzin, 1965). The Hly-positive bacteria remained sensitive to these phages. Hly factor was transmissible from these bacteria by conjugation. It appears, therefore, that at least the Hly factor used in the present study, for which we propose the name of Hly-Pzrz, is selftransmissible.

Summary The mutagenic and cytotoxic activity of two newly synthesized doxorubicin derivatives and of one daunorubicin derivative were studied in V79 Chinese hamster cells and bacteria (Salmonella typhimurium and Escherichia coli). The results showed that all the compounds tested were cytotoxic and mutagenic for both prokaryotic and eukaryotic cells. However, in both systems, the two 4-desmethoxy-and the 4'-desoxyderivatives were more active than the parent compounds, indicating that modifications in the aglycone or in the sugar moiety can produce appreciable changes in the biological properties of the anthracycline antibiotics. The in vitro activities observed in this study correlated with the in vivo antitumour potency.