In eukaryotic cells, the initial RNA transcript (pre-mRNA) contains non-coding segments called [ Select ] polymerase exons promoters spliceosomes introns that intervene between coding regions. Before the RNA leaves the nucleus, a large protein-RNA complex called the [ Select ] introns polymerase exons ribosomes spliceosomes removes these non-coding parts and joins the coding regions, known as [ Select ] spliceosomes introns polymerase exons promoters together. This process allows a single gene to encode multiple different proteins depending on which segments are treated as coding.