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In This Issue |
Pol II piece makes and breaks mRNA
"Cradle to grave" describes one protein's relationship with mRNA. As Lotan et al. reveal, the protein helps make mRNA and helps destroy it. The molecule, a piece of RNA polymerase II, might permit cells to coordinate mRNA synthesis and breakdown.
Cells degrade mRNA to eliminate damaged strands and manage protein synthesis. Enzymes first strip off the molecule's tail of multiple adenines. The demolition then sometimes proceeds from the 5' to the 3' end, usually in cytoplasmic structures called P-bodies. Or enzymes can chop up the strand in the 3'-to-5' direction. The RNA polymerase II complex weaves new strands of mRNA, but previous work by the researchers suggested that one of its components, Rpb4p, also helps initiate destruction. However, Rpb4p lacks a site for grabbing RNA, implying that it gets help.
Lotan et al. tested whether that aid comes from Rpb4p's partner, the RNA-binding protein Rpb7p. In yeast with a mutated rpb7 gene, removal of the adenine tail faltered. Moreover, the researchers found that Rpb7p gathered in P-bodies and was required for destruction of mRNA in the 5'-to-3' direction. Outside P-bodies, Rpb7p stimulated 3'-to-5' mRNA breakdown, indicating that it helps orchestrate both mRNA demolition pathways. The next question to answer, the researchers say, is whether Rpb7p links mRNA formation in the nucleus to its destruction in the cytoplasm. 
Reference:
Lotan, R., et al. 2007. J. Cell Biol. 178:1133–1143.
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