Translation in vitro of Rat Brain mRNA Coding for a Variety of Tubulin Forms

Abstract

Prenatal rat brain tubulin was resolved by isoelectric focusing into 5-6 components (isotubulins 1-6) while in mature brain 9 distinct forms were evident (isotubulins 1-9). Tubulin, isolated from various brain regions, displayed different proportions of these 9 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 5 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. Brain mRNA may consist of 5 different species coding for distinct tubulin forms. Moreover, a marked age-dependent enhancement in the relative translation of the mRNA coding for isotubulin 7 was detected which was not apparent among the translation products directed by the prenatal mRNA. Some of the age-dependent variations in tubulin microheterogeneity may be controlled at the mRNA level.