Figure 1. Schematic representation of the regulatory elements of human RNA polymerase III transcribed type 1 and type 2 genes. Nucleic acid nomenclature: R = G/A; Y = C/T; W = A/T. Designations of individual boxes are represented in appropriate color codes below type 1 and 2 gene schemes. Type 1 gene: 16 out of 17 human RNA5S genes retrieved at www.ncbi.nlm.nih.gov/nucleotide are identical; T84 within the C-box of RNA5S9 is substituted by a C. The sequence blocks of A- and C-boxes, as well as of the intermediate element (IE) in the human 5S gene are chosen by analogy to described sequence blocks in the X. laevis 5S RNA gene.129,130 The 5S gene A-box sequence lacks the conserved T in the first position of the tRNA consensus A box. The human D-box element sequence upstream of the transcription start site of the 5S gene was published.131 Type 2 genes: are representatively depicted by human tRNA consensus sequences that have been derived from published data.132-134 tRNA termination occurs at variable sites downstream of the B-box.