Degrading chloroplast mRNA: the role of polyadenylation

Chloroplast development involves changes in the stability of specific plast id mRNAs. To understand how the half-lives of these mRNAs are modified, sev eral laboratories are investigating how plastid mRNAs are degraded. This ha s led to the isolation of a high-molecular-weight complex that contains an endoribonuclease and a 3'-5' exoribonuclease, and the discovery that effici ent mRNA degradation requires polyadenylation. These findings are similar t o recent discoveries in Escherichia coli. However, an important difference between the two systems is that chloroplast mRNA degradation involves nucle ar-encoded proteins, Modification of these proteins could provide the mecha nism for altering plastid-mRNA half-lives in response to developmental stim uli.