The Determination of Posttranscriptional Modification in RNA

Significant progress has been made in recent years in recognition and understanding of the diversity of functional roles played by posttranscriptional modification in RNA (e.g., Bjork et al., 1987; Cunningham et al., 1990; Bjork et al., 1992). The functional aspects of modification have been most extensively studied in the case of tRNA (Bjork et al., 1987; Bjork et al., 1992) in which approximately 80 different posttranscriptionally modified nucleosides have been identified (Sprinzl et al., 1989; Edmonds et al., 1991). Although at an earlier time the structural characterization of modified nucleosides was usually undertaken in conjunction with their recognition during sequence determination (McCloskey and Nishimura, 1977), advances in structural methods based on mass spectrometry (McCloskey, 1991) have more recently resulted in the discovery of a number of new nucleosides in unfractionated tRNA, for which sequence locations are not yet known. We presently summarize recent progress in the development of three mass spectrometry-based methods, using instrumentation now commercially available, for the determination of posttranscriptional modification in RNA, with recent examples of their applications.