Introns alternate splicing

In addition to affecting the efficiency of promoter utilization, eukaryotic cells employ alternative RNA processing to control gene expression. This can result when alternative promoters, intron-exon splice sites, or polyadenylation sites are used. Occasionally, heterogeneity within a cell results, but more commonly the same primary transcript is processed differendy in different tissues. A few examples of each of these types of regulation are presented below. 

FIGURE 14-5 Isoforms of the rat H3 receptor. The genomic structure of the receptor (top) shows four exons (boxes, E1-E4) and three introns (bp sizes are in parentheses). Peptide sequences that correspond to translated TM regions are labeled with roman numerals (I—VII). An alternatively spliced region (orange box) is depicted between the stop sequences. Six isoforms of the receptor (labels are on the left) result from alternative splicing. (Modified with permission from reference [2].)... 

Posttranscrip-tional processing of hnRNA (pre-mRNA) None In nucleus 5 cap (7-MeG) 3 tail (poly-A sequence) Removal of introns from hnRNA Alternative splicing yields variants of protein product... 

The occurrence of several exons and intron in a gene opens the possibility of alternative splicing. 

The primary transcript of tropoelastin undergoes extensive alternative splicing. As the splitting of codons at the exon-intron borders is consistent throughout the molecule, alternative splicing occurs in a cassette-like fashion with maintenance of the coding sequence (Bashir et al, 1989). 

Figure 1. Alternatively splicing of human ATP2A1-3 genes generates multiple SERCA isoforms. Exons are represented by open boxes, introns by horizontal lines. The different splicings are indicated by lines and letters and are described in the text. Sa-Se indicate the position of stop codons of the different isoforms. Boxes in grey represent coding sequences specific for the isoforms...

Yang F, Hanson NQ, Schwichtenberg K, Tsai MY. Variable number tandem repeat in exon/intron border of the cystathionine beta-synthase gene a single nucleotide substitution in the second repeat prevents multiple alternate splicing. Am J Med Genet 2000 95 385-390. 

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