Ruth R. Painter

The effect of apholate and thiotepa on nucleic acid synthesis and nucleotide ratios in housefly eggs

Abstract The nucleic acid synthesis in normal viable housefly eggs and non-viable housefly eggs deposited by flies chemosterilized by apholate and thiotepa has been studied. During normal embryonic development, there is a rapid many-fold increase in DNA after an initial lag period. In the chemosterilized eggs there is almost no increase in DNA, but some accumulation of the deoxyribosidic components of the acid-soluble extract. The effect on the levels of RNA and ribosidic components of the acid-soluble extract is less apparent. The nucleotide ratios of normal housefly eggs has been determined to be similar to that reported for other insect eggs. Apholate-sterilized eggs were significantly lower in adenylic acid than normal fly-egg RNA. The RNA of the thiotepa sterilized eggs was a little lower in guanylic acid and contained an unidentified compound not present in normal egg RNA. When thiotepa P32 was the chemosterilant, all components of the isolated sodium RNA were labelled. This suggests that thiotepa may have been degraded and the resulting inorganic phosphate reincorporated into the RNA. There was no evidence of alkylated guanine in the RNA.

Protein synthesis by ribosomes from fertilized and unfertilized eggs of houseflies, Musca domestica

Abstract The ribosomes from unfertilized and fertilized housefly eggs have been isolated and their ability to initiate protein synthesis in a cell-free system has been investigated. There is a greater proportion of polymeric forms in the ribosomes from fertilized eggs, and these have a greater capacity to initiate protein synthesis.

Isolation and identification of egg ribosomes of the housefly, Musca domestica

Abstract Ribosomes from Musca domestica eggs have been isolated and studied. They exist in monomeric, dimeric, and polymeric forms and were identified by sucrose density-gradient separation and electron micrographs. Further studies showed that the ribosomes were sensitive to RNAse but not DNAse.

Effects of orally ingested aflatoxin B1 on nucleic acids and ribosomes of housefly ovaries

Abstract Aflatoxin B 1 was administered orally to adult Musca domestica L., and its effects on ovarian nucleic acids and ribosomes were investigated. In the ovaries of treated flies, the total rRNA content was less than normal and the rate of synthesis was slowed, as measured by the incorporation of [ 14 C]orotic acid. The metabolism of DNA was also altered as shown by the lowered incorporation of [ 3 H]thymidine 5-triphosphate into the ovarian DNA. On the other hand, the content and the synthesis of tRNA in the ovaries from aflatoxin-treated females appeared to be normal. Sedimentation analysis of fly ovarian ribosomes indicated that there was a preponderance of polymeric forms containing at least 3 ribosomal subunits. Aflatoxin B 1 did not cause disaggregation of ovarian polyribosomes. However, the incorporation of [ 14 C]orotic acid into rRNA and [ 3 H]leucine into ribosomal protein was reduced in the ovaries of aflatoxin-treated flies. Sedimentation analysis of the rRNA revealed that synthesis of the 28 S rRNA was more susceptible to the inhibition by aflatoxin B 1 than the 18 S rRNA.

Characteristics of homologous and heterologous DNA-RNA hybrids from unfertilized and fertilized eggs of houseflies, Musca domestica☆

Abstract DNA and 14C-labelled RNA were isolated from fertilized and unfertilized eggs of houseflies (Musca domestica). The two forms of nucleic acid were obtained from newly oviposited eggs and from eggs which had been incubated for 6 hours at 37°C., corresponding to the late embryonic developmental period. RNA-denatured DNA hybrids were prepared by hybridization in solution and with the DNA immobilized on membrane filters. The degree of hybridization of homologous and heterologous forms was determined by assaying the 14C-labelled RNA incorporated into the RNA-DNA hybrids. When the hybrids were formed by homologous RNA-DNA the degrees of hybridization of the forms from newly oviposited eggs and from incubated eggs were similar. A small decrease of doubtful significance was noted when heterologous hybrids were prepared from the nucleic acids of newly oviposited fertilized and unfertilized eggs. However, when heterologous hybrids were prepared from newly oviposited unfertile eggs and incubated fertile eggs, the degree of hybridization was only about 75 per cent of that found with homologous hybrids. When the hybridization involved RNA or DNA from newly oviposited fertile eggs and DNA or RNA from incubated fertile eggs, the hybridization was about 85 per cent of that for homologous hybrids.

Characteristics of DNA-RNA hybrids prepared from the eggs of normal and thiotepa chemosterilized houseflies, Musca domestica L

Abstract DNA and 14 C-labeled RNA were isolated from the eggs of normal and thiotepa chemosterilized house flies. RNA-DNA hybrids were prepared by hybridization in solution and with the DNA immobilized on membrane filters. The degree of hybridization was determined by assaying the RNA- 14 C incorporated into the RNA-DNA hybrid. The RNA from normal or chemosterilized fly eggs hybridized with the homologous form of DNA to about the same degree. However, for heterologous hybrids with RNA from one type of egg and DNA from the other, the lesser degree of hybridization indicated that only a portion of the RNA was able to recognize complementary sites in the heterologous DNA. Therefore, as a result of aziridinyl chemosterilization of the adult houseflies, both the RNA and the DNA from the eggs were altered so that they were complementary to each other, but were complementary to only a limited degree to the RNA and DNA from normal eggs.