Introns and Exons The finding of the Introns and the exons was one of the most significant discoveries in genetics in the past fifteen years. split genes were discovered when lack of relation between DNA sequences were seen during. DNA- mRNA hybridation. For all new mRNA, they must be transcribed by RNA polymerase enzymes. The transcription begins at the promoter sequence on the DNA and works down, thus the nucleotide sequence of the mRNA is complimentary to the one of DNA. In eukaryotes the mRNA is processed in the nucleus before transport to the cytoplasm for translation. In order for the mRNA to become true functioning RNA it must under go several stages of modification. At first,