Genomic structure of the human mitochondrial chaperonin genes: HSP60 and HSP10 are localised head to head on chromosome 2 separated by a bidirectional promoter

Jens J. Hansen, Peter Bross, Majken Westergaard, Marit Nielsen, Hans Eiberg, Anders D. Børglum, Jens Mogensen, Karsten Kristiansen, Lars Bolund, Niels Gregersen

Although the mitochondrial chaperonin Hsp60 and its co-chaperonin Hsp10 have received great attention in the last decade, and it has been proposed that mutations and variations in these genes may be implicated in genetic diseases, the genome structure of the human HSP60 and HSP10 genes (also known as HSPD1 and HSPE1, respectively) has not been firmly established. The picture has been confused by the presence of many pseudogenes of both HSP60 and HSP10 and the long surviving assumption that the HSP60 gene is intron-less. An earlier report on the partial sequence of the human HSP60 gene and the presence of introns has largely been overlooked. We present the full sequence of the human HSP60 and HSP10 genes. The two genes are linked head to head comprising approximately 17 kb and consist of 12 and 4 exons, respectively. The first exon of the human HSP60 gene is non-coding and the first exon of the human HSP10 gene ends with the start codon. Analysis of human and mouse expressed sequence tag sequences in GenBank indicates that alternative splicing occurs resulting in HSP60 gene transcripts with different exon-1 sequences. By sequencing of the exons, the exon/intron boundaries and the region between the two genes in 10 Danish individuals (five couples), nine nucleotide variations and one intronic deletion have been detected that, by subsequent typing of one child from each couple, have been assigned to five haplotypes. The human HSP60 gene has been localised, by radiation hybrid mapping, between markers AFMA121YH1 and WI-10756 on chromosome 2. This location and the position of two homologous fragments in the Human Genome Assembly are consistent with cytogenetic position 2q33.1. Using a luciferase-reporter assay, we demonstrate that the region between the two genes functions as a bi-directional promoter. The transcriptional activity of the promoter fragment in the HSP60 direction is approximately twice that in the HSP10 direction under normal growth conditions and, upon heat-shock, promoter activity in either direction increased by a factor of approximately 12. One of the nucleotide variations detected is localised in a putative SP1-transcription-factor-binding site in the bidirectional promoter region and analysis of the transcriptional activity of the promoter fragment with this variation has shown that it does not affect transcription levels both with and without heat-shock.