Detection of a functional promoter/enhancer in an intron-less human gene encoding a glutamine synthetase-like enzyme

A human genomic clone, psi GS, containing an intron-less glutamine synthetase (GS)-encoding pseudogene, was isolated by screening a human library. A sequence of 3004 bp, containing the GS coding region and both the 5' and 3' flanking sequences, was identified that exhibits all the characteristics of a processed pseudogene. The coding region shows 93% identity with the human GS cDNA (hGS) sequence and contains two frame-shifts and two termination codons. The coding sequence is flanked by a 9-bp AT repeat and a putative polyadenylation site, AATAAA, at the 3' end. Primer extension analysis and S1 nuclease mapping showed a transcription start point (tsp) 62 bp upstream from the start codon indicating a shorter untranslated region than hGS. Transfection of HeLa cells with cat constructs containing portions of the 5' flanking sequence showed the presence of a functional promoter/enhancer within 200 bp of the tsp, independent of its orientation.