The DNA sequence and analysis of human chromosome 6

Chromosome 6 is a metacentric chromosome that constitutes about 6% of the human genome. The finished sequence comprises 166,880,988 base pairs, representing the largest chromosome sequenced so far. The entire sequence has been subjected to high-quality manual annotation, resulting in the evidence-supported identification of 1,557 genes and 633 pseudogenes. Here we report that at least 96% of the protein-coding genes have been identified, as assessed by multi-species comparative sequence analysis, and provide evidence for the presence of further, otherwise unsupported exons/genes. Among these are genes directly implicated in cancer, schizophrenia, autoimmunity and many other diseases. Chromosome 6 harbours the largest transfer RNA gene cluster in the genome; we show that this cluster co-localizes with a region of high transcriptional activity. Within the essential immune loci of the major histocompatibility complex, we find HLA-B to be the most polymorphic gene on chromosome 6 and in the human genome.

The genome sequence of Schizosaccharomyces pombe

We have sequenced and annotated the genome of fission yeast (Schizosaccharomyces pombe), which contains the smallest number of protein-coding genes yet recorded for a eukaryote: 4,824. The centromeres are between 35 and 110 kilobases (kb) and contain related repeats including a highly conserved 1.8-kb element. Regions upstream of genes are longer than in budding yeast (Saccharomyces cerevisiae), possibly reflecting more-extended control regions. Some 43% of the genes contain introns, of which there are 4,730. Fifty genes have significant similarity with human disease genes; half of these are cancer related. We identify highly conserved genes important for eukaryotic cell organization including those required for the cytoskeleton, compartmentation, cell-cycle control, proteolysis, protein phosphorylation and RNA splicing. These genes may have originated with the appearance of eukaryotic life. Few similarly conserved genes that are important for multicellular organization were identified, suggesting that the transition from prokaryotes to eukaryotes required more new genes than did the transition from unicellular to multicellular organization.

The chromosome 6 sequencing project at the Sanger Centre

Chromosome 6 is probably best known for encoding the major histocompatibility complex (MHC) which is essential to the human immune response. In addition, it has been shown to be associated with many diseases such Schizophrenia, Diabetes, Arthritis, Haemochromatosis, Narcolepsy, Epilepsy, Retinitis Pigmentosa, Deafness, Ovarian Cancer, and many more. Chromosome 6 is about 180 Mb in size and is estimated to encode around 3500 genes of which only about 10% are currently known. It is our aim to map, sequence and annotate the entire chromosome in close collaboration with the chromosome 6 community.

Large-scale sequence comparisons reveal unusually high levels of variation in the HLA-DQB1 locus in the class II region of the human MHC

Comparison of genomic sequences flanking the HLA-DQB1 locus in the human MHC class II region reveals local sequence variation of up to 10%, which is the highest level of sequence variation found in the human genome so far. The variation is haplotype-specific and extends far beyond the transcriptional unit of the DQB1 gene, suggesting hitch-hiking along with functionally selected alleles as the most likely mechanism. All major insertions/deletions (indels) were found to be of retroviral origin and in the immediate upstream region of DQB1. Possible cis-acting effects of these indels on the transcriptional regulation of DQB1 are discussed.

Severe non-ketotic hyperosmolar coma--intensive care management

We report a case of non-ketotic hyperosmolar coma, which presented with blood sugar levels far exceeding any previously recorded in the literature. The patient developed acute renal failure, probably because of rhabdomyolysis, which was successfully managed with continuous veno-venous haemofiltration. He developed blurring of vision resulting from biochemical changes, which was managed conservatively. We discuss the mechanisms of causation of the renal failure and visual blurring.