Genes in pieces

Enlarged view of an adenovirus particle. The viral capsid is an icosahedron with 12 antenna-like fiber projections that function to attach the virus to the cell surface during infection. The viral DNA is packaged inside the particle.

 The DNA molecule is used as a template to synthesize a precursor mRNA. This RNA is a linear copy of the template DNA and contains both exon and intron sequences.
 In contrast, the mature mRNA only consists of exon sequences. The introns (A, B and C) are cut out and the exons are joined together by a process called RNA splicing.