The universal regulatory mechanism in eukaryotes for controlling gene expression includes a. control of the processing of mrna after it is transcribed from dna but before it leaves the nucleus, and control of the rate it leaves the nucleus. b. control of the genes transcribed and the rate they are transcribed. c. control of mrna in the cytoplasm after it leaves the nucleus, including changes to mrna before translation begins. d. control of polypeptides after they have been synthesized but before they are functional. e. all of these mechanisms are used; there is no single universal mechanism.