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This paper describes two ecdysone-deficient, recessive-lethal mutants,lethal(1)giant ring gland (grg) andlethal(1)suppressor of forked (mad-ts: Jürgens and Gateff 1979) and compares their ecdysteroid titers with that of the wild-type. Mutant larvae show a much reduced ecdysteroid content, amounting to 1/10 to 1/30 of the wild-type values, but never a true titer peak. They fail to pupate and die after 1-3 weeks. Ecdysteroid feeding elicits different responses in the larvae of the two mutants.mad-ts larvae pupate within 24 h, thus showing that their low ecdysteroid titer is directly connected to their inability to pupate.mad-ts resembles the mutantlethal (3)ecdysone-1 (Garen et al. 1977). Thegrg mutant larvae, on the other hand, fail to pupate after 20-hydroxyecdysone feeding as well as injection. The primary defect of thegrg mutant is not entirely clear. Thegrg larval salivary gland cells appear to possess normal ecdysteroid receptors. Furthermore, the low ecdysteroid titer ingrg is not the result of an increased ecdysteroid catabolism. The primary defect in the mutant may lie in the malfunctioning neurosecretory cells which do not show neurosecretion in histological preparations. Further support for this notion comes from electronmicrographs of the enlargedgrg ring glands which, in contrast to the wild-type, do not possess nerve endings.In the wild-type three ecdysteroid peaks were found: one shortly before puparium formation, the second at approximately 12 h and the third at about 30 h after pupation. The ecdysteroid titer peak in late third instar, wild-type larvae is mainly due to the presence of 20-dydroxyecdysone as shown by radioimmunoassays after thin layer chromatography and derivatization followed by gas liquid chromatography and mass spectroscopy. In addition, a number of unidentified polar and apolar metabolites were also present.

Testicular cells of male mice were isolated, and the incorporation of tritium labeled thymidine into the DNA of the cells was estimated after exposure to various chemical mutagens. The normal semiconservative DNA synthesis was suppressed by the addition of hydroxyurea. Thirteen compounds were tested. Unscheduled DNA synthesis (UDS) was stimulated by ethyl methanesulfonate (EMS), methyl methanesulfonate (MMS), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and triaziquone, and, to a lesser extent, by 4-nitroquinoline 1-oxide (4-NQO), mitomycin C, ICR-191 and nitrogen mustard (HN-2). No thymidine incorporation could be estimated after incubation of the cells with 9-aminoacridine, hydroxyurethane, alpha-naphthylamine, 2-acetylaminofluorene (AAF) nor with N-hydroxy-2-acetylaminofluorene (N-OH-AAF).

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Three new double‐stranded polydeoxyribonucleotides containing the nucleoside analogs 6‐thiodeoxyguanosine and 6‐thiodeoxyinosine were synthesized enzymatically. Poly[d(A‐C) · d(T‐s6G)] and poly[d(A‐s6G) · d(T‐C)] were prepared by extensive synthesis with DNA polymerase from Micrococcus luteus, while the same enzyme from Escherichia coli failed in extensive polymerisation but brought about the synthesis of poly[d(T‐s6G)] and poly[d(T‐s6I)] by the repair mechanism using single‐stranded poly[d(A‐C)] template and a minute amount of d(T‐G)n primer. The analog‐containing DNAs were characterized by ultraviolet absorption and circular dichroism spectra as well as by their stability against thermal and alkaline denaturation. The substitution by 6‐thiodeoxyguanosine or 6‐thiodeoxyinosine for deoxyguanosine reduces the stability of the biopolymers considerably. Exchange of the analog‐containing strand by singlestranded poly[d(T‐G)] takes place rapidly even at ambient temperature.