Emeritus Associate Professor of Biochemistry and Biophysics
(PhD – Cornell University)
Nucleocytoplasmic Transport and RNA–Protein Interactions
Eukaryotic cells are host to a profuse array of small, stable RNA-protein complexes (RNPs) that carry out essential functions in, e.g., RNA processing, RNA modification, telomere maintenance, and gene regulation. The RNA and protein components of these RNPs are synthesized in separate subcellular compartments, the nucleus and cytoplasm, respectively. How and where do the individual components of small RNPs get together and assemble with one another? Does assembly follow a defined order? Is assembly cooperative, ensuring that one component will assemble only when another is also present? Except for a few cases, the pathways of small RNP assembly are not well delineated; still less is known about possible cooperative interactions that may regulate assembly.
As a model system to investigate RNP assembly, we are investigating the biogenesis of of the mammalian signal recognition particle (SRP), a ubiquitous, phylogenetically conserved, RNP that delivers proteins to the cell’s protein translocation apparatus. Animal SRP consists of six proteins and a 300 nucleotide RNA. Since SRP functions in the cytoplasm, SRP RNA must be exported from the nucleus. Current evidence indicates that SRP assembles in the nucleus and we are identifying the transport receptors that move SRP proteins into the nucleus and SRP out of the nucleus.
We are also using a variety of biochemical approaches to determine whether assembly of SRP proteins onto SRP RNA involves cooperative interactions. We have evidence that the two largest SRP proteins do bind the RNA cooperatively and are currently determining what other interactions exist among the remaining proteins. This information will enable us to determine whether there is a defined order of assembly.
Given its rather modest molecular complexity (only seven components), determining the mechanism by which SRP assembles is well within reach and will add to our understanding of nuclear transport and ribonucleoprotein biogenesis generally. Also, SRP is essential for cell viability, so deciphering how SRP assembles could provide a new entry point for managing cell growth.
- Jeffries, CD, Fried, HM, and Perkins, DO (2010). Additional Layers Of Gene Regulatory Complexity From Recently Discovered microRNAs Mechanisms. Int’l J. Biochem. & Cell Biol. 42: 1236–1242.
- Jeffries, CD, Fried, HM, and Perkins, DO (2011). Nuclear and cytoplasmic localization of neural stem cell microRNAs. RNA, 17: 675-686.
- Maity TS, Fried HM, Weeks KM. Anti-cooperative assembly of the SRP19 and SRP68/72 components of the signal recognition particle. Biochem J. 2008 Jun 18.
- Maity TS, Leonard CW, Rose MA, Fried HM, Weeks KM. Compartmentalization directs assembly of the signal recognition particle. Biochemistry. 2006 Dec 19;45(50):14955-64.