Nucleotide sequence and transcription of a human glycine tRNA_GCC gene and nearby pseudogene

A bacteriophage λ clone containing a 15.4-kb human DNA fragment was isolated and found to contain a glycine tRNA gene and, 758 bp away, a pseudogene, both with an anticodon of GCC. The nucleotide (nt) sequence of a 1362-bp segment of this clone, encompassing the gene, pseudogene, and their flanking regions, was determined. The gene and pseudogene have an identical sequence of eight nt (5′-CAGCTGGA-3′) in their 5′-flanking regions immediately preceding the coding regions, as well as characteristic transcription termination sites of five consecutive T nt in the 3′-flanking regions. Neither of these genes has intervening sequences. Only one of the two genes was efficiently transcribed in vitro by RNA polymerase III in a HeLa cell-free system. During the course of transcription, primary transcripts of one gene wereb processed to yield mature-sized products. In contrast, the level of transcription of the second gene was significantly less than that of the first, and no mature-sized products could be detected. The nt sequence of the inefficiently transcribed gene has two base substitutions compared to the sequence of the efficiently transcribed gene, and the DNA sequence predicted from the human placental tRNA_GCC^Gly sequence. One of these nt substitutions is a C to T transition in the TTCG sequence within the B block of the characteristic internal split promoter sequence. The precursor-product relationships of the tRNA transcripts were established by comparing the RNase T₁ and RNase A fingerprints of the precursors and products.