Alternative exon combination can lead to different
primary hnRNA transcript includes both exon-
& intron-equvialent sequences. The exon-equivalents
(numbered) may correspond to functional regions of the
protein, for example, DNA-binding regions or dehydrogenase
activity. By removing one or more exon-equivalent regions
along with the intron-equivalents, different proteins with
different functions can be produced.
Alternative splicing may explain
why genomes can get along with far fewer protein-coding
regions than expected.