The identification and characterisation of a novel Apoptotic Gene,Snama, in drosophila melanogaster

[摘要] SNAMA is the Drosophila melanogaster homologue of a group of proteins that areknown to bind p53 and the retinoblastoma protein (Rb). This multi domain proteinconsists of a conserved N-terminal domain called Domain With No Name (DWNN),a zinc finger, a cysteine rich RING finger-like domain, a probable p53 bindingregion, and a glutamic acid-rich and lysine-rich region. These associated domainsindicate that SNAMA plays an important regulatory role in the cell and may functionin RNA processing and in apoptosis.The DWNN domain was first identified in Cytotoxic T-cell resistant Chinese hamsterovary (CHO) cells using promoter trap mutagenesis to screen for genes involved inapoptosis. Subsequently, this domain was identified in other eukaryotic organismsincluding animals and plants.The SNAMA transcriptional unit consists of 9 exons and 8 introns that code for a1231 amino acid protein with the 76 residue N-terminal DWNN domain. The DWNNdomain has a 23.5% sequence identity to the ubiquitin protein and a predicted foldedstructure similar to ubiquitin. Western blots identified multiple bands indicative ofubiquitin tagged proteins. Taken together this suggests a role in the ubiquitin pathwayeither as an ubiquitin domain protein or the DWNN domain of SNAMA tagging otherproteins. The cysteine rich RING finger-like domain has a histidine to serinesubstitution at the fourth position of the putative RING finger and represents a distinct class of RING finger-like proteins that could have ubiquitin ligase activity.Northern blot analysis identified a single 4.6 kbp transcript expressed abundantlythroughout development early in embryogenesis but reduced in older embryos and inadult male and females. SNAMA probably interacts with Dmp53 as a suppressor ofapoptosis or a negative regulator of an activator of apoptosis. It is a vital generequired for development, as the mutant P-element insertion line in which the Pelementis inserted in the first intron of SNAMA is lethal when homozygous.Acridine orange staining of these mutant flies showed a direct correlation between thepresence of SNAMA and apoptosis. An increase in the levels of apoptosis occurred inembryos with relatively low levels of SNAMA expression. The mode of this action iseither direct, or via other proteins that are involved in the apoptotic pathway.

[发布机构] University of the Witwatersrand