The fate of an intervening sequence RNA: Excision and cyclization of the Tetrahymena ribosomal RNA intervening sequence in vivo

Abstract

Previous studies of RNA splicing in vitro, showed that intervening sequence (IVS) of the Tetrahymena rRNA precursor is excised as a unique linear RNA molecule and subsequently cyclized. The occurrence and stability of these RNA species were investigated in vivo. RNA was separated by gel electrophoresis, transferred to diazotized paper, and hydridized with 32P-labeled DNA probes. RNA molecules containing the IVS were found to reside within the nucleus and not in the cytoplasm. The species found in the nucleus include both the linear and circular forms of the excised IVS RNA, as well as the unspliced precursor. On the basis of quantitation of the hybridization, the half-lives of the IVS-containing pre-rRNA and the excised IVS RNA in rapidly growing cells were estimated as 2 and 6 s, respectively. Splicing is not a rate-limiting step in rRNA maturation and that the IVS RNA is quickly degraded after its excision. When the deproteinized nuclear RNA was incubated at 37.degree. C in a Mg2+-containing solution, a substantial portion of the linear IVS RNA was converted to the circular form. Autocyclization, prevously characterized with IVS RNA produced by splicing in vitro, is therefore also a property of IVS RNA produced in vivo.