From DNA conformation to processing of messenger RNA.

The relevance of the DNA molecule resides in that it carries all the genetic information within the cell. A molecule that directs and controls the expression of its encoded information through the interaction with other cellular components, is obviously compelled to display a full complement of salient features. First, the direct involvement of DNA in rather elaborate biological processes requires of the molecule to be structurally dynamic. Second, it appears that most eukaryotic genes are discontinuous. Their encoded information is interrupted by noncoding sequences which are transcribed along with the coding regions into full precursor RNA molecules. Since mature messenger RNA molecules are known to be substantially smaller that their corresponding primary nuclear transcripts, besides exhibiting chemical modifications, the latter must be subjected to coordinate processing steps to become fully functional in the cell. Indeed, mRNA molecules are derived from nuclear precursors through a variety of posttranscriptional chemical reactions involving end-terminal additions, excision of nonsense regions and orderly ligation of the coding sequences. The aim of this review is to emphasize the biological relevance of the conformational versatility of DNA and to address and discuss recent progress in messenger RNA processing in eukaryotes.