Splicing process

FIGURE 14.23 RNA splicing in TetraAjimejta rRNA matnradon (a) the gnanosine-mediated reaction involved in the antocatalytic excision of the Tetrahymena rRNA intron, and (b) the overall splicing process. The cyclized intron is formed via nncleophilic attack of the 3 -OH on the phosphodiester bond that is 15 nncleotides from the 5 -GA end of the spliced-ont intron. Cyclization frees a linear 15-mer with a 5 -GA end. 

Can direct evidence of the splicing process be obtained by electron microscopy The answer is positive, as shown in Figure 10.14, the micrographs obtained utilizing... 

Figure 10.14 Electron micrographs showing vesicle splicing process after oleate addition. (From Stano et al, in press.)...

The exact mechanism by which Rev interferes with the transport and splicing process is largely unknown. One possible scenario is that Rev interacts with components of the spliceosome, which leads to the release of splice factors that allow cytosolic transport without actual splicing. 

Specific proteins have been found in this complex, including the splicing-associated factors SRml60, DEK, and RNPS1, the mRNA-associated shuttling protein Y14 and the mRNA export factor Aly (also called REF) (Kim et al., 2001 Le Hir et al., 2000a Zhou et al., 2000). The Y14 and REF proteins have no known function in the splicing process, but they have both been linked to mRNA export (Kataoka et al., 2000 Stutz et al., 2000 Zhou et al., 2000). 

The splicing of nascent mRNA molecules is a complicated process. It requires the cooperation of several small RNAs and proteins that form a large complex called a spliceosome. However, the chemistry of the splicing process is simple. 

Small nuclear RNAs complexed with protein (snRNPs) [e.g., U1 and U2] are involved in the cleavage and splicing process. A lariat structure may be generated during the splicing reaction (see Figure 3-20). 

Fig. 5.3. Debranching of lariats. Comparison of splicing products before and after a debranching reaction analysed in a 6% gel containing 1 x TBE. Products obtained from a standard splicing reaction (-D lane) is co-electrophoresed with the same reaction that has been debranched by an additional treatment in S100 extract (+D lane). Identities of individual bands are indicated schematically. Filled boxes, cross-hatched boxes and thin lines denote the 5 - and 3 -exons and intron, respectively. Note that only small amounts of the lariats become debranched under the splicing process, probably due to protection of the branch site by splicing factors. After deproteination, debranching becomes a very efficient process linearising more than...

Ans. The base sequence in ptRNA is the complement of that in template DNA (keep in mind that U is used in RNA instead of T). The direction of RNA synthesis proceeds in the opposite direction of the template DNA strand. In the splicing process, introns are removed and the results are mRNA. 

The G143A mutation will significantly affect the splicing process from pre-mRNA to mature mRNA if a type I intron is present after codon 143 in the cyt b gene. 

The intron is eliminated in its lariat form and is subsequently degraded. The splicing process that generates functional transalpts is termed functional splicing. 

While a lot of detail has been worked out about the splicing process by means of biochemistry and molecular biology, it had not received much attention from the field of chemical biology. 

---