Book Viewer

Short Contents | Full Contents | Other books @ NCBI

| Modern Genetic Analysis Chapter 3. Gene Function Making Functional Transcripts Figure 3-9. Processing of primary transcript. (a) Transcription is mediated by RNA polymerase. (b) Early in transcription an enzyme, guanyltransferase, adds 7-methylguanosine (m7Gppp) to the 5 end of the mRNA. (c) The sequence AAUAAA, near the 3 end, helps signal a cleavage event (d) by an endonuclease approximately 20 bp farther downstream. (e) An enzyme, poly(A) polymerase, then adds a poly(A) tail, made up of 150 to 200 adenosine residues, to the site of this cleavage at the 3 end. (f) This yields the complete primary mRNA. (From J. E. Darnell, Jr., "The Processing of RNA." Copyright © 1983 by Scientific American, Inc. All rights reserved.)

© 1999 by W. H. Freeman and Company. All rights reserved.