Using Saccharomyces cerevisiae as a Model to Investigate the Role of Human NAD Kinase

Christopher Shane Ramey
University of California, Los Angeles

When Escherichia coli cells growing at their optimum growth conditions experience a sudden downshift in temperature, growth halts while a specific set of “cold-shock” proteins (CSPs) are transiently induced to higher levels. CSPs are thought to play an important role in cellular adaptation for gene expression and growth at cold temperatures, and their synthesis increases during the first hour after cells are shifted to low temperatures. One CSP, cold-shock DEAD-box Protein A (CsdA), is induced approximately 15-fold in E. coli shifted from 37°C to 15°C, and is essential for cell growth at cold temperatures. CsdA belongs to a family of ATP-dependent RNA helicases that contain the highly conserved Asp-Glu-Ala-Asp (D-E-A-D) amino acid sequence motif and are believed to be involved in unwinding RNA secondary structures. Since RNA secondary structures are stabilized at cold temperatures, which might account (in part) for the halt in E. coli cell growth at such temperatures, CsdA induction suggests the necessity for increased RNA helicase activity. For example, unwinding highly stable mRNA secondary structure would allow the ribosome to regain access to the mRNA and resume translation. This could also explain why CsdA is essential for cold temperature growth. Similarly, CsdA might assist ribosome biogenesis by enabling ribosomal RNAs to fold into conformations necessary for ribosome assembly or by playing a role in the maturation of ribosomal RNA precursors. My work currently addresses both of these aspects of CsdA function, at the molecular as well as biochemical level.