[The length of polyadenylic acid tracts of Sindbis virus RNA: the possible existence of two synthetic mechanisms].

The poly (A) tracts of RNA's from viral particles and from replicative complex belong to two classes of 180 and of 60 nucleotides in length. Those of the mRNA are homogenous and around 280 nucleotides in length. The results presented here strongly suggest the possibility of a copying mechanism in the first case and of a posttranscriptional addition in the latter.