The intervening sequence of a mouse beta-globin gene is transcribed within the 15S beta-globin mRNA precursor.

Abstract
Mouse .beta.-globin is encoded in a discontinuous structural gene interrupted by a 550 base pair intervening sequence of DNA. The mature .beta.-globin mRNA appears to be synthesized via a 15S precursor, the length of which roughly equals the total length of the coding and intervening sequences of the .beta.-globin gene. Using the electron microscope to visualize hybrid structures formed between this gene and the purified 15S .beta.-globin mRNA precursor, the intervening sequence is shown to be present within the larger precursor molecule. The precursor mRNA is evidently processed through the removal and rejoining of internal RNA sequences.