Reflections on the history of pre-mRNA processing and highlights of current knowledge: A unified picture

Abstract

Several strong conclusions emerge concerning pre-mRNA processing from both old and newer experiments. The RNAPII complex is involved with pre-mRNA processing through binding of processing proteins to the CTD (carboxyl terminal domain) of the largest RNAPII subunit. These interactions are necessary for efficient processing, but whether factor binding to the CTD and delivery to splicing sites is obligatory or facilitatory is unsettled. Capping, addition of an m 7 Gppp residue (cap) to the initial transcribed residue of a pre-mRNA, occurs within seconds. Splicing of pre-mRNA by spliceosomes at particular sites is most likely committed during transcription by the binding of initiating processing factors and ∼50% of the time is completed in mammalian cells before completion of the primary transcript. This fact has led to an outpouring in the literature about "cotranscriptional splicing." However splicing requires several minutes for completion and can take longer. The RNAPII complex moves through very long introns and also through regions dense with alternating exons and introns at an average rate of ∼3 kb per min and is, therefore, not likely detained at each splice site for more than a few seconds, if at all. Cleavage of the primary transcript at the 3 ′ end and polyadenylation occurs within 30 sec or less at recognized polyA sites, and the majority of newly polyadenylated pre-mRNA molecules are much larger than the average mRNA. Finally, it seems quite likely that the nascent RNA most often remains associated with the chromosomal locus being transcribed until processing is complete, possibly acquiring factors related to the transport of the new mRNA to the cytoplasm.

Negative Feed-forward Control of Tumor Necrosis Factor (TNF) by Tristetraprolin (ZFP36) Is Limited by the Mitogen-activated Protein Kinase Phosphatase, Dual-specificity Phosphatase 1 (DUSP1)

“…We interpret this to mean that although actinomycin D prevents RNA polymerase II-dependent transcription, the rapid build-up of unspliced/unprocessed TNF RNA (see Fig. 2B) allows the ongoing production of mature TNF mRNA to continue briefly following the addition of actinomycin D. This interpretation is consistent with the fact that splicing and processing to produce mature mRNAs can take several minutes or often longer (37). Thus, the actinomycin D chase experiments should more accurately be considered as reflecting post-transcription RNA processing and maturation as well as mRNA degradation.…”

A quantitative 14-3-3 interaction screen connects the nuclear exosome targeting complex to the DNA damage response

“…1B). These included the NEXT complex subunits RBM7, ZCCHC8, and MTR4 (Lubas et al 2011); the CPSF2 and CPSF3 components of the mRNA cleavage and polyadenylation complex (CPSF) (Darnell 2013); the EIF4E and ZNF598 subunits of the 4EHP-GIGYF complex involved in translational repression (Morita et al 2012); and the NELF-E, NELF-C/D, and NELF-B subunits of the NELF complex that controls transcription elongation (Nechaev and Adelman 2011).…”

Systematic analysis of intron size and abundance parameters in diverse lineages

“…The related fields have now agreed upon a unified picture [36] and the spatiotemporally organized movements of cellular components within the nucleus, between the nucleus and the cytosol, and among the subcellular organelles and structures are of essence for the understanding of cellular physiology. In such a context, minimal introns are most relevant to the nuclear architectures and their dynamics [6,37].…”