PHOTOREACTIVATION OF RNA IN UV‐IRRADIATED INSECT EGGS (SMITTIA SP., CHIRONOMIDAE, DIPTERA) I. PHOTOSENSITIZED PRODUCTION AND LIGHT‐DEPENDENT DISAPPEARANCE OF PYRIMIDINE DIMERS*

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Abstract
Irradiation of Smittia eggs with UV during intravitelline cleavage causes the formation of pyrimidine dimers in the (largely ribosomal) RNA of the eggs. The yield of dimers is wavelength‐dependent in a way that strongly suggests the involvement of photosensitizing egg components. Illumination of UV‐irradiated eggs with light (380 or 400 nm) causes both photoreactivation of the eggs and mono‐merization of the pyrimidine dimers in their RNA. The photoreactivable sector of the biological damage is correlated with the amount of pyrimidine dimers present in the RNA after inactivation of the eggs with UV of different wavelengths. The data are regarded as the first direct evidence that the photoreactivation of a eukaryotic organism is correlated with the light‐dependent (and apparently enzymatic) monomerization of pyrimidine dimers in RNA.