Processing of Capped Intronless Pre-mRNA (Homo sapiens)
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Description
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.
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. View original pathway at:Reactome.</div>
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DataNodes
intronless pre-mRNA:CBC
complexIntronless Histone
pre-mRNA:CBP80:CBP20:SLBP:ZFP100 ComplexIntronless Histone
pre-mRNA:CBP80:CBP20:SLBPHistone pre-mRNA:CBC
complexHistone pre-mRNA:CBC:ZFP100
Complexintronless pre-mRNA:CBC
complexIntronless transcript derived Histone
mRNA:SLBP:CBP80:CBP20derived mRNA
complextranscript derived Histone pre-mRNA:CBC
complexpre-mRNA:CBC
complexintronless mRNA
fragmentmRNA
fragment:CPSF:PAP:PABPN1 complexAnnotated Interactions
intronless pre-mRNA:CBC
complexintronless pre-mRNA:CBC
complexIntronless Histone
pre-mRNA:CBP80:CBP20:SLBP:ZFP100 ComplexIntronless Histone
pre-mRNA:CBP80:CBP20:SLBP:ZFP100 ComplexIntronless Histone
pre-mRNA:CBP80:CBP20:SLBPIntronless Histone
pre-mRNA:CBP80:CBP20:SLBPHistone pre-mRNA:CBC
complexHistone pre-mRNA:CBC
complexHistone pre-mRNA:CBC:ZFP100
ComplexHistone pre-mRNA:CBC:ZFP100
Complexintronless pre-mRNA:CBC
complexintronless pre-mRNA:CBC
complexIntronless transcript derived Histone
mRNA:SLBP:CBP80:CBP20derived mRNA
complextranscript derived Histone pre-mRNA:CBC
complexCleavage is preceded by the assembly of a large processing complex, the composition of which is poorly defined. ATP, but not its hydrolysis, is required for assembly. Cleavage depends on a number of protein factor. CPSF, a heterotetramer, binds specifically to the AAUAAA sequence. The heterotrimer CstF binds the GU- or U-rich downstream element.
pre-mRNA:CBC
complexintronless mRNA
fragmentmRNA
fragment:CPSF:PAP:PABPN1 complex