Processing of Capped Intronless Pre-mRNA

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R-HSA-75067
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Homo sapiens
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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.
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.

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.

Literature References
PubMed ID Title Journal Year
12242288 The stem-loop binding protein is required for efficient translation of histone mRNA in vivo and in vitro

Sanchez, R, Marzluff, WF

Mol Cell Biol 2002
11031238 Cajal bodies: the first 100 years.

Gall, JG

Annu Rev Cell Dev Biol 2001
10571029 Formation of the 3' end of histone mRNA.

Dominski, Z, Marzluff, WF

Gene 1999
12408966 The human and mouse replication-dependent histone genes

Marzluff, WF, Gongidi, P, Woods, KR, Jin, J, Maltais, LJ

Genomics 2002
7597053 Coiled bodies contain U7 small nuclear RNA and associate with specific DNA sequences in interphase human cells.

Frey, MR, Matera, AG

Proc Natl Acad Sci U S A 1995
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