Kohn R E, Duerr J S, McManus J R, Duke A, Rakow T L, Maruyama H, Moulder G, Maruyama I N, Barstead R J, Rand J B
Program in Molecular and Cell Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA.
Mol Biol Cell. 2000 Oct;11(10):3441-52. doi: 10.1091/mbc.11.10.3441.
The Caenorhabditis elegans UNC-13 protein and its mammalian homologues are important for normal neurotransmitter release. We have identified a set of transcripts from the unc-13 locus in C. elegans resulting from alternative splicing and apparent alternative promoters. These transcripts encode proteins that are identical in their C-terminal regions but that vary in their N-terminal regions. The most abundant protein form is localized to most or all synapses. We have analyzed the sequence alterations, immunostaining patterns, and behavioral phenotypes of 31 independent unc-13 alleles. Many of these mutations are transcript-specific; their phenotypes suggest that the different UNC-13 forms have different cellular functions. We have also isolated a deletion allele that is predicted to disrupt all UNC-13 protein products; animals homozygous for this null allele are able to complete embryogenesis and hatch, but they die as paralyzed first-stage larvae. Transgenic expression of the entire gene rescues the behavior of mutants fully; transgenic overexpression of one of the transcripts can partially compensate for the genetic loss of another. This finding suggests some degree of functional overlap of the different protein products.
秀丽隐杆线虫的UNC-13蛋白及其哺乳动物同源物对于正常神经递质释放至关重要。我们已鉴定出秀丽隐杆线虫unc-13基因座产生的一组转录本，这些转录本源于可变剪接和明显的可变启动子。这些转录本编码的蛋白质在其C末端区域相同，但在N末端区域有所不同。最丰富的蛋白质形式定位于大多数或所有突触。我们分析了31个独立的unc-13等位基因的序列改变、免疫染色模式和行为表型。这些突变中的许多是转录本特异性的；它们的表型表明不同的UNC-13形式具有不同的细胞功能。我们还分离出一个缺失等位基因，预计该等位基因会破坏所有UNC-13蛋白产物；该无效等位基因的纯合动物能够完成胚胎发育并孵化，但它们会作为瘫痪的第一阶段幼虫死亡。整个基因的转基因表达完全挽救了突变体的行为；一种转录本的转基因过表达可以部分补偿另一种转录本的基因缺失。这一发现表明不同蛋白质产物存在一定程度的功能重叠。
