Figure 1

Schematic representation of the human ASS gene and the ASS-EGFP transgene. (A) Structure of the human ASS gene. Human ASS gene composes of 16 exons with the initiation codon (ATG) residing in exon 3 and the termination codon (TGA) in exon 16. There are two poly(A) signals, pA1 and pA2, residing in exon 16 to produce ASS mRNA of 1.7 kb and 2.7 kb. UTR: untranslated region. (B) Structure of the Tg(ASS-Ex3-EGFP) transgene. The EGFP coding sequence is inserted right after the initiation codon of the ASS gene. Transcription initiated from the ASS promoter is terminated by a SV40 poly(A) signal, pAsv, residing immediate downstream of the EGFP gene. EGFP but not ASS protein is produced from this transgene. (C) Structure of the Tg(ASS-Ex16-EGFP) transgene. EGFP is inserted in exon 16 between the termination codon and pA1 of the ASS gene. Depending on which poly(A) signal is used, bicistronic mRNAs of 3.1 kb and 4.1 kb are produced. A sequence of IRES (internal ribosome entrance site) is inserted in front of EGFP to facilitate EGFP protein translation. Both ASS and EGFP proteins are produced from this transgene.