Fig. 2. Transgene constructs used to localize cardiac and skeletal muscle regulatory elements associated with the mouse Bop gene. (A) Structure of the 5' region of the mouse Bop gene. The Bop gene contains two first exons that code for the amino termini of Bop gene products expressed in T lymphocytes (tBOP) and striated muscle (mBOP). These exons, which are separated by an intron of 70 kb, are spliced to a common second exon located 22 kb downstream of mBop exon 1. Other more 3' protein coding exons are not shown. White boxes denote 5' untranslated exon sequence and black boxes denote protein-coding exon sequence. The position of the muscle regulatory region upstream of mBop exon 1 is shown in red. (B) Regions of 5' flanking DNA immediately upstream of mBop exon 1 used to create lacZ transgenes are shown. Nucleotides are numbered relative to the transcriptional start site, which is designated `0'. Construct number is indicated on the left, and the corresponding expression pattern is summarized on the right. All constructs, except construct 4, contain the indicated upstream genomic regions fused to the hsp68 basal promoter and the lacZ gene. Construct 4 contains the region from –986 to +75 bp fused directly to promoterless lacZ. The MEF2 site was mutated in constructs 5 and 6, and the three E-boxes were mutated in construct 7. Asterisk denotes constructs that were also used to generate stable transgenic lines. The numbers of F0 transgenic embryos compared with the total number of transgene-positive embryos are shown.