mRNA turnover is a precisely controlled process whose regulation is critical for the modulation of gene expression in response to changing environmental and physiological conditions. A major pathway for the decay of bulk mRNA in the cells is the 5’ to 3’ pathway wherein following polyadenylation, mRNAs are decapped and then subjected to 5’ to 3’ exonucleolytic degradation. The hetero-octameric Lsm1-7-Pat1 complex (made of the Lsm1 through Lsm7 subunits and Pat1 subunit) is conserved in all eukaryotes and plays a key role as an activator of decapping in this pathway. Lsm1 and Pat1 are the key distinguishing subunits of this complex.
Expression of the trait specified by any gene (DNA) requires the production of an RNA copy of that gene and in most cases also the further decoding of that RNA copy into protein. Cells precisely control the degree to which each gene is expressed using a variety of mechanisms. One of them is by regulating the life time of the RNA copy. We study the ways in which RNA life time is regulated in the cells and the cellular machinery that mediates such regulation, a protein complex called Lsm1-7-Pat1 complex, in particular.
Being a very fundamental process, misregulation of RNA lifetime control is known to be associated with a large variety of diseases. Malfunction of the Lsm1-7-Pat1 complex is implicated in several cancers and neurodegenerative disorders. Some of these are known to have a higher incidence among veterans than civilians.
“Misregulation of the Lsm1-7-Pat1 complex is associated with several types of cancers and neurodegenerative disorders like leukoencephalopathy. Therefore understanding the mechanism of function of this complex will provide insights to develop novel approaches for therapeutic interventions.”
We use purification and subsequent biochemical analyses to determine the underlying structural and/or functional defect in the Lsm1-7-Pat1 complex in the diseased cells (Affinity purification, protein-RNA and protein-protein interaction assays).
Our studies on the relationship of Lsm1-7-Pat1 to RNA destruction and degradation bring us a step closer to understanding cancer.
We showed earlier that this complex specifically associates with oligoadenylated mRNAs and targets them for decapping in vivo. Using a combination of genetic studies and biochemical analysis of the purified Lsm1-7-Pat1 complex, we showed that this complex has an intrinsic ability to distinguish between oligoadenylated and polyadenylated mRNA. Our studies further revealed the parts of Lsm1 that are critical for RNA binding, complex formation and recognition of poly(A) tail length and showed that the RNA binding surface of the Lsm1-7-Pat1 complex is composite made of residues from both the Lsm1-7 complex and the Pat1 subunit. Importantly, our studies also revealed that in the case of Lsm1 (unlike in other Lsm proteins), the C-terminal extension also carries an RNA binding surface and therefore is essential for the function of the Lsm1-7-Pat1 complex.
Additional studies have also shown that the poly(A) binding protein (PABP) could inhibit deadenylation and regulate the interaction of the Lsm1-7-Pat1 complex with the mRNA. The mechanism of such interplay between PABP and the Lsm1-7-Pat1 complex in mRNA decay is not known. Further, human Lsm1 is an oncogene when over expressed and how the misregulation of the Lsm1-7-Pat1 complex leads to oncogenesis is not understood. The mechanisms of these processes are our current focus.