Saebøe-Larssen S, Lyamouri M, Merriam J, Oksvold M P, Lambertsson A
Department of Biology, University of Oslo, Norway.
Genetics. 1998 Mar;148(3):1215-24. doi: 10.1093/genetics/148.3.1215.
Minutes comprise > 50 phenotypically similar mutations scattered throughout the genome of Drosophila, many of which are identified as mutations in ribosomal protein (rp) genes. Common traits of the Minute phenotype are short and thin bristles, slow development, and recessive lethality. By mobilizing a P element inserted in the 5' UTR of M(3)95A, the gene encoding ribosomal protein S3 (RPS3), we have generated two homozygous viable heteroalleles that are partial revertants with respect to the Minute phenotype. Molecular characterization revealed both alleles to be imprecise excisions, leaving 40 and 110 bp, respectively, at the P-element insertion site. The weaker allele (40 bp insert) is associated with a approximately 15% decrease in RPS3 mRNA abundance and displays a moderate Minute phenotype. In the stronger allele (110 bp insert) RPS3 mRNA levels are reduced by approximately 60%, resulting in an extreme Minute phenotype that includes many morphological abnormalities as well as sterility in both males and females due to disruption of early gametogenesis. The results show that there is a correlation between reduced RPS3 mRNA levels and the severity of the Minute phenotype, in which faulty differentiation of somatic tissues and arrest of gametogenesis represent the extreme case. That heteroalleles in M(3)95A can mimic the phenotypic variations that exist between different Minute/rp-gene mutations strongly suggests that all phenotypes primarily are caused by reductions in maximum protein synthesis rates, but that the sensitivity for reduced levels of the individual rp-gene products is different.
“分钟”（Minute）包含超过50个表型相似的突变，这些突变散布在果蝇的基因组中，其中许多被鉴定为核糖体蛋白（rp）基因的突变。“分钟”表型的共同特征是刚毛短而细、发育缓慢和隐性致死性。通过激活插入在M(3)95A（编码核糖体蛋白S3，即RPS3）5'非翻译区的P因子，我们产生了两个纯合可存活的异源等位基因，它们是“分钟”表型的部分回复突变体。分子特征分析表明，这两个等位基因都是不准确的切除产物，在P因子插入位点分别留下了40和110个碱基对。较弱的等位基因（40个碱基对插入）与RPS3 mRNA丰度降低约15%相关，并表现出中度的“分钟”表型。在较强的等位基因（110个碱基对插入）中，RPS3 mRNA水平降低了约60%，导致极端的“分钟”表型，包括许多形态异常以及由于早期配子发生中断导致的雄性和雌性不育。结果表明，RPS3 mRNA水平降低与“分钟”表型的严重程度之间存在相关性，其中体细胞组织分化异常和配子发生停滞代表了极端情况。M(3)95A中的异源等位基因能够模拟不同“分钟”/rp基因突变之间存在的表型变异，这强烈表明所有表型主要是由最大蛋白质合成速率降低引起的，但不同rp基因产物水平降低的敏感性不同。
