Refers to the location of the exon-intron junctions in a pre-mRNA (i.e., the primary transcript that must undergo additional processing to become a mature RNA for translation into a protein). Splice sites can be determined by comparing the sequence of genomic DNA with that of the cDNA sequence. In mRNA, introns (non-protein coding regions) are removed by the splicing machinery; however, exons can also be removed. Depending on which exons (or parts of exons) are removed, different proteins can be made from the same initial RNA or gene. Different proteins created in this way are “splice variants” or “alternatively spliced”.