Evidence for channeled diffusion of pre-mRNAs during nuclear RNA transport in metazoans.
We report studies using an enhanced experimental system to investigate organization of nuclear pre-mRNA metabolism. It is based on the powerful genetic system and polytene nuclei of Drosophila. We observe (at steady state) movement of a specific pre-mRNA between its gene and the nuclear surface. This movement is isotropic, at rates consistent with diffusion and is restricted to a small nuclear subcompartment defined by exclusion from chromosome axes and the nucleolus. Bulk polyadenylated nuclear pre-mRNA precisely localizes in this same subcompartment indicating that most or all pre-mRNAs use the same route of intranuclear movement. In addition to association with nascent transcripts, snRNPs are coconcentrated with pre-mRNA in this subcompartment. In contrast to constitutive splices, at least one regulated splice occurs slowly and may undergo execution remotely from the site of pre-mRNA synthesis. Details of our results suggest that retention of incompletely spliced pre-mRNA is a function of the nuclear surface. We propose a simple model--based on channeled diffusion--for organization of intranuclear transport and metabolism of pre-mRNAs in polytene nuclei. We argue that this model can be generalized to all metazoan nuclei.
Zachar
Z
Z
Department of Biochemistry and Cell Biology, University of New York, Stony Brook 11794-5215.
Kramer
J
J
Mims
I P
IP
Bingham
P M
PM
D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D004277:DNA, Single-Stranded; D004058:Diffusion; D004171:Diploidy; D004330:Drosophila; D005796:Genes; D007438:Introns; D007700:Kinetics; D012322:RNA Precursors / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012326:RNA Splicing; D015138:RNA, Nuclear / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism; D014158:Transcription, Genetic
D004277:DNA, Single-Stranded; D012322:RNA Precursors; D015138:RNA, Nuclear; D017411:Ribonucleoproteins, Small Nuclear