Transcription and translation. These two processes are closely coupled in prokaryotes whereas they are spatially and temporally separate in eukaryotes. (A) In prokaryotes, the primary transcript serves as mRNA and is used immediately as the template for protein synthesis. (B) In eukaryotes, mRNA precursors are processed and spliced in the nucleus before being transported to the cytoplasm for translation into protein.

[Information from J. Darnell, H. Lodish, and D. Baltimore. Molecular Cell Biology, 2d ed. (Scientific American Books, 1990), p. 230.]