Regulation of prenatal and postnatal protein synthesis in mouse brain.

Abstract

Regulation of protein synthesis during prenatal and postnatal brain development was examined using postmitochondrial supernatant (PMS) fractions and isolated ribosome-pH 5 enzyme systems from fetal, neonatal, and adult neural tissue. The rate of polyuridylic acid (poly-U)-dependent protein synthetic activity was inversely proportional to the endogenous rate of protein synthesis in either the PMS fractions or ribosomal preparations. A careful analysis of the kinetics of the poly-U-dependent polypeptide synthesis revealed that there was a lag in the time at which certain of the PMS preparations could begin to utilize the poly-U template as sole source of mRNA. The lag period was dependent upon the developmental age of the neural tissue used and the Mg2+ concentration of the protein synthesis reaction. Since previous work reported that the observed developmental decrease in the rate of polypeptide synthesis utilizing a poly-U template could not be measured by several isolation techniques to determine if the purification procedure might have affected the ribosomes in some manner by removing a specific protein(s) involved in ribosome-cytosol interactions. At 6 mM-Mg2+ the rate of poly-U-dependent protein synthesis was inversely proportional to the rate of endogenous synthesis and depended upon the method used to isolate the ribosomes: microsomes congruent to Triton X-100-treated < DOC-treated < KCl-treated. However, there was no age-dependent effect with any of the ribosomal preparations. The data suggest that there is a developmental modulating effect of ribosomal activity in PMS preparations which is not found in association with the isolated ribosome-pH 5 enzyme protein synthesizing system.