Structural and functional characterization of mitochondrial EndoG, a sugar non-specific nuclease which plays an important role during apoptosis.

Combining sequence analysis, structure prediction, and site-directed mutagenesis, we have investigated the mechanism of catalysis and substrate binding by the apoptotic mitochondrial nuclease EndoG, which belongs to the large family of DNA/RNA non-specific betabetaalpha-Me-finger nucleases. Catalysis of phosphodiester bond cleavage involves several highly conserved amino acid residues, namely His143, Asn174, and Glu182 required for water activation and metal ion binding, as well as Arg141 required for proper substrate binding and positioning, respectively. These results indicate that EndoG basically follows a similar mechanism as the Serratia nuclease, the best studied representative of the family of DNA/RNA non-specific nucleases, but that differences are observed for transition state stabilisation.

Endonuclease G: a mitochondrial protein released in apoptosis and involved in caspase-independent DNA degradation.

A hallmark of apoptosis is the fragmentation of nuclear DNA. Although this activity involves the caspase-3-dependent DNAse CAD (caspase-activated DNAse), evidence exists that DNA fragmentation can occur independently of caspase activity. Here we report on the ability of truncated Bid (tBid) to induce the release of a DNAse activity from mitochondria.

Elements regulating differential activity of chicken histone H1 gene promoters.

The chicken genome contains six closely related histone H1 genes, each of which encodes a different H1 protein. The four common regulatory elements previously identified in H1 histone promoters are very similar in sequence and location in all chicken H1 genes, which gives rise to the question of how the six H1 variants are expressed at significantly different levels. Transient transfections of reporter gene transcriptional fusions indicate that approximately 200 bp of each promoter is sufficient to generate the observed spectrum of H1 promoter activity.

Characterization and expression of the mouse endonuclease G gene.

Endonuclease G (Endo G) is a nuclease of prokaryotic lineage found in the mitochondria of vertebrates that has been suggested to play a role in mitochondrial DNA (mtDNA) replication. We have isolated and sequenced the entire mouse endo G gene, determined the limits of the mRNA, and mapped the promoter region. The coding sequence of the single copy gene is interrupted by two introns and analysis of the transcripts does not support a model by which more than one Endo G isoform could be produced by alternative splicing.

Initiation binding repressor, a factor that binds to the transcription initiation site of the histone h5 gene, is a glycosylated member of a family of cell growth regulators [corrected].

Initiation binding repressor [corrected] (IBR) is a chicken erythrocyte factor (apparent molecular mass, 70 to 73 kDa) that binds to the sequences spanning the transcription initiation site of the histone h5 gene, repressing its transcription. A variety of other cells, including transformed erythroid precursors, do not have IBR but a factor referred to as IBF (68 to 70 kDa) that recognizes the same IBR sites. We have cloned the IBR cDNA and studied the relationship of IBR and IBF.