Synthesis of tubulin and actin by neuronal and glial nuclear preparations from devloping rat brain.

A system was established in which nuclear preparations from rat brains were capable of protein synthesis under cell-free conditions. The electrophoretic pattern of the synthesized proteins was similar to that found in vivo provided that the reaction mixture contained pH 5 precipitated factors derived from the high speed supernatant fraction of brain. In the absence of the pH 5 factors, using nuclear preparations from brains of 2-day-old rats, approximately 1.5% and 2% of the newly synthesized proteins were identified as tubulin and actin, respectively. In the presence of pH 5 factors, protein synthesis was stimulated and the proportion of the newly synthesized tubulin and actin increased to 26% and 11%, respectively. In contrast to nuclear fractions from 2-day-old rats, when nuclei from brains of 1-month-old rats were tested in the presence of pH 5 factors, the proportion of tubulin and actin synthesized was lower and amounted to 10% and 4%, respectively. The age-dependent change in the relative amount of the tubulin and actin synthesized is in good agreement with the translational pattern shown by brain polyribosomes in a brain cell-free system as well as with the pattern obtained with brain mRNA translated in a wheat germ cell-free system. Nuclei enriched for either neuronal or glial populations synthesized similar proportions of tubulin and actin in vitro. We conclude that the reduction in the synthesis of tubulin and actin during the postnatal development of the rat brain occurs in both neuronal and glial cells.