Finally, there is the modular nature of the enhancer and silencer units that control whether and where and how long a particular gene product is expressed (reviewed in Davidson, 2001, 2006; see also Prud’homme et al., 2007, Chapter 6, this volume).
Mutational events that affect either the structure or the presence/ absence of particular domains within the encoded gene product or that affect the transcriptional modular units must influence how the respective genes are used in particular recruitment events. An example is the use of alternative v domains in the adhesion protein CD44 (Ruiz et al., 1995),), which can dramatically alter specific cellular capabilities of the expressing cells. The ubiquity of alternative splicing as a source of functionally altered proteins (Xing and Lee, 2006), however, serves as a general indicator of the importance of alterations in domain structure and composition as an input to regulatory change (Alonso and Wilkins, 2005). With respect to