Elongation factor-1 alpha (EF-1$ alpha$) is a ubiquitous, highly conserved protein, that functions in peptide elongation during mRNA translation. A cDNA, S1, was isolated in rat; its predicted amino acid sequence shares high similarity (92.6%) with mouse and human EF-1$ alpha$. The principal objective of this thesis is the molecular characterization of S1, a member of the mammalian EF-1$ alpha$ gene family. We have cloned an EF-1$ alpha$ cDNA in rat, and showed that rat S1 and rat EF-1$ alpha$ are two different mRNAs that share extensive sequence similarity in the coding region, but differ considerably in their noncoding regions. The 3$ sp prime$ noncoding regions of S1 and EF-1$ alpha$ were subcloned into the pGEM3z plasmid and cRNA probes were synthesized using an in vitro transcription method. Northern analysis and RNase protection assays have shown that S1 mRNA can only be detected in rat and mouse brain, heart, and muscle, whereas EF-1$ alpha$ mRNA can be detected in all tissues. These results were confirmed by non-radioactive in situ hybridization. A strong S1-positive signal was detected in the hippocampus, cerebral cortex, medulla, and cerebellum of rat brain, whereas liver sections were negative. Certain cells, such as Purkinje neurons in the cerebellum, and motor neurons of the lower brain stem, were S1-positive. On the other hand, EF-1$ alpha$ mRNA was detected in all cell types that we have examined so far. These results prompted us to hypothesize that S1 is a terminal differentiation-specific EF-1$ alpha$ isoform, whose expression is limited to permanently growth-arrested cells. We tested this hypothesis by investigating the expression of S1 and EF-1$ alpha$ during rat development. S1 upregulation correlates with the terminal differentiation process during in vivo neurogenesis and myogenesis. Furthermore, S1 expression is dependent upon the formation of multinucleated myotubes during myogenesis in culture. EF-1$ alpha$ mRNA levels are down-regulated

Wang, Eugenia (Supervisor)