Elongation factor-1 alpha (EF-1 alpha) is an ubiquitous protein that functions in peptide elongation during mRNA translation. We previously reported the isolation of a rat S1 protein that is antigenically related to statin, a nonproliferation-specific protein; this S1 gene shares a high degree of homology to EF-1 alpha. We constructed specific riboprobes to the two genes, based on the difference in the 3' noncoding regions of both S1 and EF-1 alpha mRNAs. Northern analysis and RNase protection assays have revealed that S1 mRNA is present only in brain, heart, and muscle, while EF-1 alpha mRNA has been detected in all tissues surveyed so far. The same tissue specificity has been observed in mouse, suggesting that S1 expression is conserved between these two mammalian species. S1 transcript was detected in late brain embryogenesis (day 20), but in lower amounts than in 3-month-old adult brain. We show that the relative levels of both S1 and EF-1 alpha transcripts and their respective tissue abundances remain unchanged during the aging process. The function of S1 is not yet known; but these results suggest that it may be involved in specific control mechanisms for protein synthesis in tissues where cells (i.e. neurons and myocytes) are permanently locked in a state of nonproliferation.