Maurice Leo Errera

Ultraviolet reactivation and ultraviolet mutagenesis of λ in different genetic systems

Abstract The lex + function is necessary for the induction of clear mutations of bacteriophage λ by ultraviolet irradiation. Ultraviolet reactivation of λ phage is also dependent on the lex + function. Ultraviolet mutations are affected to a small extent by the red + function of λ phage whereas this function seems to play an important role in the spontaneous mutation process.

The role of the nucleolus in ribonucleic acid-and protein synthesis. I. Incorporation of cytidine into normal and nucleolar inactivated HeLa cells.

Abstract Nucleoli of HeLa cells growing in tissue culture were selectively irradiated with an u.v. microbeam and the subsequent incorporation of [3H]cytidine into the ribonucleic acid of the nucleolus, extra-nucleolar parts of the nucleus, and the cytoplasm, was studied by autoradiography. Comparison with cells containing normal nucleoli revealed that approximately 2 3 of the cytoplasmic incorporation is directly dependent on the nucleolus, but that less than 1 3 of the incorporation into extra-nucleolar parts of the nucleus is dependent on the nucleolus. These results when combined with quantitative kinetic studies of cytidine incorporation strongly support the hypothesis that a major part of the ribonucleic acid of the cytoplasm is synthesized in the nucleolus.

Chloramphenicol-sensitive DNA synthesis in normal and irradiated bacteria.

Addition of chloramphenicol, immediately after irradiation, to cultures of E. coli B, irradiated with doses of u.v., such as so inhibit DNA synthesis for about 40 min, prevents the subsequent DNA synthesis in the cells, as long as the inhibitor is present in the medium. In the non-irradiated, but chloramphenicol-treated culture, there is a temporary but diminished synthesis of DNA. After removal of the inhibitor, DNA synthesis recovers both in the control and in the irradiated cells. If chloramphenicol is added 35 min after irradiation to the culture, the antibiotic does not prevent the recovery of DNA synthesis.

A SENSITIVE METHOD FOR MEASURING PYRIMIDINE DIMERS IN SITU

Abstract. –An immunocytological method for detecting pyrimidine dimers in situ has been developed. The technique is based on the fixation in cell nuclei of radiolabelled antibodies directed against ultraviolet irradiated DNA. The relative amount of bound antibodies was estimated by radioautography. Pyrimidine dimers induced by a dose as low as 2 J m‐2 can easily be detected. With this technique, the dose response of DNA photoproducts and their elimination by excision and photoreactivation were followed in eukaryotic cell cultures.

Chromosome and chromatid exchanges in chinese hamster cells

Chromosomes were studied by autoradiography in a mixed culture of diploid and tetraploid cells, after having induced fusion with Sendai virus between two Chinese hamster cell populations, one labelled with 3H-, the other with 14C-thymidine; sister chromatid exchanges were studied in the 3H diploid cells and exchanges between chromosomes in the 3H-14C tetraploid synkaryons. In both cases, the frequency of exchanges increases after U. V. irradiation.

The uptake of [8-14C]adenine and [2-14C]phenylalanine by rat-liver nuclei in vitro

Abstract 1. 1. Normal rat liver nucleic have been shown to take up [8- 14 C]adenine and [2- 14 C]phenylalanine in vitro . 2. 2. Nuclei, prepared from regenerating rat liver 24, 48 and 72 hours after partial hepatectomy, take up labelled adenine and phenylalanine in vitro . The nucleic acid metabolism of the isolated nuclei of regenerating rat liver recovers much more rapidly from the effects of partial hepatectomy than does the protein metabolism. 3. 3. The cytoplasmic fractions of rat liver enhance the uptake of adenine and phenylalanine. The microsomes appear to influence the uptake of adenine by isolated nuclei, while the uptake of phenylalanine appears to be influenced by the mitochondria.

The effect of X-rays and ultraviolet light on the uptake in vitro of [8-14C]adenine and [2-14C]-phenylalanine by isolated nuclei

Abstract 1. 1. The uptake of [8-14C]adenine and [2-14C]phenylalanine into isolated calfthymus nuclei have been shown to be inhibited by X-irradiation. 2. 2. X-irradiation of isolated calf-thymus nuclei inhibited the uptake of [14C]adenine into the nuclear RNA while the uptake into the DNA was unaffected. 3. 3. X-irradiation of isolated rat liver nuclei and/or microsomes inhibited the uptake of [14C]adenine by the nuclei. u.v. irradiation of the nuclei and/or the microsomes, in this system, gave rise to an inhibition of adenine uptake which was reversed by incubating in daylight. 4. 4. X-irradiation of isolated rat-liver nuclei and/or mitochondria inhibited the uptake of [14C]phenylalanine by the nuclei. u.v. irradiation of the nuclei and/or the microsomes, in this system, gave rise to an inhibition of phenylalanine uptake which was reversed by incubating in daylight.

The rôle of the nucleolus in ribonucleic acid- and protein synthesis. II. Amino acid incorporation into normal and nucleolar inactivated hela cells

Abstract The kinetics of incorporation of amino acids into the different parts of growing HeLa cells indicate that the process begins at a comparable rate in the nucleolus, in the rest of the nucleus, and in the cytoplasm. Therefore there seems in our circumstances to be no direct relationship between nucleoside uptake and amino acid uptake. If the nucleolus is irradiated with a u.v. microbeam, with a dose such as to inhibit almost completely cytidine incorporation, a partial effect (30% inhibition) on amino acid uptake in this organelle only becomes apparent after a period of incubation of 6 h. In these conditions there is no change in amino acid incorporation into the rest of the nucleus, but there is a 30% drop in amino acid incorporation into the cytoplasm, indicating some remote control of the nucleolus on cytoplasmic protein metabolism.

Kinetics of pulse-labeling of ribonucleic acid in HeLa cells

Abstract HeLa cells have been submitted to short tritiated nucleoside pulses, and their radioactivity has been followed in the nucleus minus nucleolus (N), in the nucleolus (n) and in the cytoplasm (C) after various incubation times in unlabeled media. The independent uptake of these nucleosides into the nucleus minus nucleolus and the nucleolus has been confirmed — and part of this radioactivity is transferred from both these cell parts into the cytoplasm. However, the cytoplasmic gain is greater than the nuclear loss of grains. Cytoplasmic ribosomal RNA is probably formed from precursors synthesized in the nucleus and nucleolus, but it is not known whether this RNA undergoes any rearrangement during its transfer to the cytoplasm. Messenger RNA constitutes probably also an important fraction of the RNA label transferred from the nucleus to the cytoplasm.

EFFECTS OF X-RAYS ON RNA AND RNA METABOLISM IN HELA CELLS.

Abstract The effect of X-rays on RNA and RNA metabolism has been studied. 1. 1. When prelabelled cells were irradiated, RNA was radiosensitive when it had just been formed. The nucleolar RNA seemed more sensitive than that of the rest of the nucleus. 2. 2. When irradiated cells were incubated in [ 3 H]cytidine, the uptake of the label in RNA was considerably more depressed for short incubation times, indicating that the damage to the mechanism of RNA synthesis can be repaired. 3. 3. When prelabelled cells were irradiated and then transferred to a non-radioactive medium, the transfer of label from nuclear to cytoplasmic RNA was also inhibited.