Originally published as Genetics Published Articles Ahead of Print on February 16, 2005.

Genetics, Vol. 170, 33-46, May 2005, Copyright © 2005
doi:10.1534/genetics.104.034322

Mutations in the Saccharomyces cerevisiae LSM1 Gene That Affect mRNA Decapping and 3' End Protection

Sundaresan Tharun^*,1, Denise Muhlrad, Ashis Chowdhury^* and Roy Parker

^* Department of Biochemistry, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799
Department of Molecular and Cellular Biology and Howard Hughes Medical Institute, University of Arizona, Tucson, Arizona 85721

¹ Corresponding author: Department of Biochemistry, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814-4799.
E-mail: tsundaresan{at}usuhs.mil

The decapping of eukaryotic mRNAs is a key step in their degradation. The heteroheptameric Lsm1p–7p complex is a general activator of decapping and also functions in protecting the 3' ends of deadenylated mRNAs from a 3'-trimming reaction. Lsm1p is the unique member of the Lsm1p–7p complex, distinguishing that complex from the functionally different Lsm2p–8p complex. To understand the function of Lsm1p, we constructed a series of deletion and point mutations of the LSM1 gene and examined their effects on phenotype. These studies revealed the following: (i) Mutations affecting the predicted RNA-binding and inter-subunit interaction residues of Lsm1p led to impairment of mRNA decay, suggesting that the integrity of the Lsm1p–7p complex and the ability of the Lsm1p–7p complex to interact with mRNA are important for mRNA decay function; (ii) mutations affecting the predicted RNA contact residues did not affect the localization of the Lsm1p–7p complex to the P-bodies; (iii) mRNA 3'-end protection could be indicative of the binding of the Lsm1p–7p complex to the mRNA prior to activation of decapping, since all the mutants defective in mRNA 3' end protection were also blocked in mRNA decay; and (iv) in addition to the Sm domain, the C-terminal domain of Lsm1p is also important for mRNA decay function.

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