Cell-free synthesis of the myelin basic proteins in a wheat germ system programmed with brain messenger RNA.

Poly A(+) messenger RNA (mRNA) was isolated from the brains of 3-week-old mice and translated in a cell-free system derived from wheat germ. Maximal stimulation of the system by brain mRNA was observed at a relatively low K+ concentration (45 mM) and low mRNA concentration (1-10 microgram/ml). The translational system was dependent on an energy-generating system and stimulated by the addition of spermidine and transfer RNA. Under optimal conditions, incorporation was linear for almost 45 min, but the overall stimulation with brain mRNA was relatively low (about twofold). In spite of the low stimulation, analysis of the translation products indicated that in the presence of brain mRNA polypeptides which co-chromatographed and co-electrophoresed with the two mouse myelin basic proteins could be detected. In control experiments with liver poly A(+) mRNA, which stimulated the translational system to a greater extent than brain mRNA, no such polypeptides could be detected. In this system the ratio of synthesis of small myelin basic protein to large myelin basic protein was found to be about 4.0, which correlates well with that found in vivo.