Comparison of tRNA activity under homologous and heterologous conditions during the reproductive cycle of Heteropneustes fossilis.

Rate of protein synthesis in ovary is analyzed throughout the annual reproductive cycle of H. fossilis. It is highest during previtellogenic phase and lowest during post spawning phase. The variation pattern matches with aminoacylation capacity of tRNA. The aminoacylation capacity of tRNA is compared in the two phases under homologous and heterologous conditions. Both tRNA and aRS are obtained from the same phase under homologous conditions and from different phases under heterologous conditions. Aminoacylation capacity is also compared in ovary and liver under homologous and heterologous conditions. Both tRNA and aRS show higher activity in previtellogenic phase. However, tRNA contributes more for higher aminoacylation activity. Transfer RNA fractionates into similar isoacceptors during the two phases. This indicates that the primary structure of tRNA may not change during the reproductive cycle. Therefore, it is suggested that the difference in aminoacylation activity may be due to post-transcriptional modifications of tRNA leading to conformational changes. Gm modification and 2-O' methylation of tRNA are reported earlier to vary during the reproductive cycle [2]. The results support the earlier suggestion of conformational changes in tRNA in 'active' and 'inactive' forms in previtellogenic and post spawning phases respectively. Aminoacylation capacity of tRNA shows organ specificity. It is high in ovary than in liver. Poor aminoacylation capacity is shown under heterologous conditions. This may be due to incompatible aRS related to specific amino acid pool in the tissue, or post transcriptional changes in tRNA, which may not allow cross acylation with full efficiency.