Translation in vitro of rat brain mRNA coding for a variety of tubulin forms

Prenatal rat brain tubulin was resolved by isoelectric focusing into five to six components (isotubulins 1--6) while in mature brain nine distinct forms were evident (isotubulins 1--9). Tubulin, isolated from various brain regions, displayed different proportions of these nine isotubulins which may result from the heterogeneity in brain cell population. Mature brain mRNA, when translated in vitro, in the reticulocyte lysate cell-free system, directed the synthesis of five tubulin forms, namely isotubulins 1, 3, 4 (or 5), 6 and 7. The mRNA species coding for isotubulins 3 and 7 could be partially separated on formamide/sucrose gradients, while in the absence of formamide the mRNA species directing the synthesis of isotubulins 1, 4 (or 5) and 6 showed differences in mobility. It therefore appears that brain mRNA may consist of five different species coding for distinct tubulin forms. Moreover, a marked age-dependent enhancement in the relative translation of the mRNA coding for isotubulin 7, which is not apparent among the translation products directed by the prenatal mRNA, was detected. Our results indicate that some of the age-dependent variations in tubulin microheterogeneity may be controlled at the mRNA level.