[Ratio of the amounts of the mRNA poly A+/poly A- fractions in the myocardium and the life span of mRNA poly A+].

Two mRNA fractions, poly A+ and poly A- were found in the rat heart muscle. They comprise 30 and 70% of the entire mRNA, respectively. The ratio of the mRNA poly A+ to poly A- in the myocardium does not change in physiological aging. According to the kinetics of labelled precursor incorporation into mRNA, the life span of the main mass of mRNA poly A+ in the myocardium is about 4 hours.