Novel Structure of the 5 ' End Region of the Human

The structure of the 5 ' end region of the human argininosuccinate synthetase (AS) gene was analyzed in detail. The 5 ' flanking region up to 350 nucleotides from the putative transcription initiation site is unusually G + C rich (80%). Three repeats of a CCGCCC sequence and one complementary GGGCGG sequence are present in this region. It contains no CCAAT box-like sequence, but does contain one typical TATA box and a 20 bases-long inverted repeat sequence that could form a stem and loop structure just upstream from the TATA box. An octanucleotide sequence, AGAAGTGA, found in the 5 ' flanking region of the AS gene is also, commonly present in those regions of the two other human genes expressed mainly in the liver. These structural features of the AS gene indicate that it shares common structures with two completely different groups of genes, i.e. tissue-specific genes and housekeeping ones. Moreover, two enhancer core-like sequences, alternating purine-pyrimidines tracts and two independent Alu type highly repetitive sequences are apparent in the first intron of the AS gene. Argininosuccinate synthetase (AS) [L-citrulline: to be highest in the liver (7). The human genom