Fluorescence in situ hybridization and chromosomal organization of the human Sirtuin 7 gene
Sirtuin 7 (SIRT7) is a member of the sirtuin family of protein deacetylases and is, therefore, a derivative of yeast Silent information regulator 2 (SIR2). SIR2 and its mammalian orthologs play an important role in epigenetic gene silencing, DNA recombination, cellular differentiation and metabolism, and the regulation of aging. In contrast to most sirtuins, SIRT7 does not exert characteristic NAD+-dependent deacetylase activity. We have isolated and characterized the human Sirt7 genomic sequence, which spans a region of 6.2 kb and which has one single genomic locus. Determination of the exon/intron splice junctions found the full-length SIRT7 protein to consist of 10 exons ranging in size from 71 bp (exon 4) to 237 bp (exon 7). The human Sirt7 open reading frame encodes a 400-aa protein with a predictive molecular weight of 44.9 kDa and an isoelectric point of 9.80. Characterization of the 5' flanking genomic region, which precedes the Sirt7 open reading frame, revealed a TATA- and CCAAT-box less promoter that lacks CpG islands. A number of AML-1 and GATA-x transcription factor binding sites were found, which remain to be further evaluated experimentally. Fluorescence in situ hybridization analysis localized the human Sirt7 gene to chromosome 17q25.3; a region which is frequently affected by chromosomal alterations in acute leukemias and lymphomas. Human SIRT7 appears to be most predominantly expressed in the blood and in CD33+ myeloid bone marrow precursor cells, while the lowest levels are found in the ovaries and skeletal muscle. Functional characteristics of SIRT7 are essentially unknown at present and remain to be further elucidated.