Table 1.

Summary of the in vivo activity of the enhancer

Construct	TG	ES	ET	NO
HHXK	14	9	2	5
tkXK	13	6	0	7
KXtk	12	7	2	5
tkNcXb	15	9	8	5
tk-	9	0	1	8

Abbreviations are as in Fig. 1. Data are presented as numbers of embryos.