NniDi

EGF precursor gene

FIGURE 13-22 Genes made up of parts of other genes. The LDL receptor (the plasma low density lipoprotein receptor) gene contains a stretch of six exons closely related to sin exons from the C9 complement gene, and eight dosefy related to eight from the EgF (epidermal growth factor) precursor gene. Thus, the LDL receptor gene ts made up of exons shuffled between other genes; and, though not shown here, these same parts appear tn yet other genes as well. The introns are, in many cases, not positioned in exactly the same positions within the EGF precursor gene and the comparable region of the LDL receptor gene. When they are in the same plate, this is indicated by dotted lines.

use of the 5r and 3' splice sites—guarantees that almost all recombinant genes will be expressed, because the splice sites in different genes are largely interchangeable. In addition, alternative splicing can allow new exons to be tried without discarding the original gene product.

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