SUB-CELLULAR LOCALISATION OF ENHANCED LYSINE INCORPORATION INTO CEREBRAL CORTEX PROTEINS IN DARK-REARED AND LIGHT-EXPOSED RATS

Incorporation of lysine into acid-insoluble material from subcellular fractions of rat cerebral cortex has been studied using double and single-labelling techniques, in littermates reared for 50 days in the dark and then dark-maintained or light-exposed for 1 h. When light-exposed animals were compared to dark controls the only subcellular fraction from the whole cortex in which lysine incorporation shows a significant elevation (168%, P < 0.05) was located in the ribosomal pellet of the cerebral cortex. A similar comparison of subcellular fractions from visual and motor cortices showed that the elevation was again in the ribosomes and confined to visual cortex only. Motor cortex of light-exposed animals showed a small depression of incorporation in ribosomes as compared to dark controls. Sub-fractionation of nuclei from whole cortex preparations showed varying, but non-significant elevations in light-exposed animals in all but the histone fraction in which there was negligible incorporation of precursor. It is concluded that enhancement of incorporation of precursor into proteins of the cerebral cortex, which accompanies first exposure to light, is a complex response. At exposure for 1 h it involves a number of particular protein species located in the visual cortex, a major proportion of which are ribosomally bound.