Modulation of poly(A)(+)mRNA-metabolizing and transporting systems under special consideration of microtubule protein and actin.

At present, three enzymes are known which participate in regulation of polyadenylation and polydeadenylation of eukaryotic mRNA: poly(A) polymerase, endoribonuclease IV and 2',3'-exoribonuclease. Moreover, poly(A)-associated proteins as well as the cytoskeletal proteins actin and tubulin have been found to be involved in poly(A) metabolism of mRNA; their modulation effects on poly(A) metabolizing enzyme systems will be described in greater detail. Nucleo-cytoplasmic transport of poly(A)-containing mRNA is thought to be mediated by nuclear-envelope nucleoside triphosphatase. The stimulation of this enzyme by the poly(A) segment of mRNA and its modulation by microtubule protein are discussed in the second part of this review.