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

Mouse beta-globin in encoded in a discontinuous structural gene interrupted by a 550-base pair intervening sequence of DNA. Correspondingly, 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, we show that the intervening sequence is present within the larger precursor molecule. This finding suggests that the precursor mRNA is processed through the removal and rejoining of internal RNA sequences.