SLBP Dependent Processing of Replication-Dependent Histone Pre-mRNAs SLBP independent Processing of Histone Pre-mRNAs Processing of Capped Intronless Pre-mRNA Authored: Marzluff, WF, 2003-08-22 00:29:39 Co-transcriptional pre-mRNA splicing is not obligatory. Pre-mRNA splicing begins co-transcriptionally and often continues post-transcriptionally. Human genes contain an average of nine introns per gene, which cannot serve as splicing substrates until both 5' and 3' ends of each intron are synthesized. Thus the time that it takes for pol II to synthesize each intron defines a minimal time and distance along the gene in which splicing factors can be recruited. The time that it takes for pol II to reach the end of the gene defines the maximal time in which splicing could occur co-transcriptionally. Thus, the kinetics of transcription can affect the kinetics of splicing.<br> There are two classes of intronless pre-mRNAs (mRNAs expressed from genes that lack introns). The first class encodes the replication dependent histone mRNAs. These mRNAs have unique 3' ends that do not have a polyA tail. The replication dependent histone mRNAs in all metazoans, as well as Chlamydomonas and Volvox fall into this class. <p>The second class of mRNAs end in polyA tails, which are formed by a mechanism similar to that which poly-adenylate pre-mRNAs containing introns. In the intronless genes there is a different method of replacing the 3' splice site that activates polyadenylation. Edited: Joshi-Tope, G, 0000-00-00 00:00:00 GENE ONTOLOGYGO:0031124 Pubmed10571029 Pubmed11031238 Pubmed12242288 Pubmed12408966 Pubmed7597053 Reactome Database ID Release 4375067 Reactome, http://www.reactome.org ReactomeREACT_1768 Processing of Intronless Pre-mRNAs PathwayStep78 PathwayStep84 PathwayStep75