RNA Poly(A) Site Selection in Plants and Animals

A critical process in gene expression is pre-mRNA 3′end cleavage and subsequent adding of a poly(A) tail. To investigate the poly(A) site selection in different organisms, we mapped the poly(A) sites in eighteen animals and seven plants that had their genomes sequenced. The pre-mRNA nucleotide (the poly(A) tail starting position) corresponding to the first adenosine of poly(A) tail was found to be typically an adenosine. For the RNA nucleotide (the poly(A) tail attachment position) to which the poly(A) tail was attached, C and U were strongly preferred over G in plants, but most animals preferred G over U. Dinucleotides UA or CA was preferred at the poly(A) sites in most species. However, C was still preferred at the attachment position in the absence of the dinucleotide CA. When the poly(A) tail starting position was not an adenosine, C/G ratios in animals, dicot plants, and monocot plants are different at the poly(A) tail attachment position. Base composition patterns in the regions nearby the poly(A) sites were also characterized and will be presented.