Ulery T L, Mangus D A, Jaehning J A
Department of Biology, Indiana University, Bloomington 47405.
Mol Gen Genet. 1991 Nov;230(1-2):129-35. doi: 10.1007/BF00290660.
We have found that many laboratory strains of yeast are defective in galactose metabolism owing to a recessive mutation in the previously characterized nuclear gene, IMP1. This defect leads to a requirement for mitochondrial function for growth on, and metabolism of, galactose. Genetic background affects the degree to which cells are defective. In particular, alleles of GAL3 affect the ability to score the Imp phenotype. We have found that in imp1 strains, transcriptional induction of the galactose inducible genes (GAL1, 2, 7 + 10, MEL1) is normal, but galactose transport is reduced in both rho+ and rho0 cells. This phenotype is normally associated with mutations in GAL2, the galactose permease. Although the growth phenotypes of gal2 and imp1 mutants are distinct, we found that the transformation of imp1 rho0 strains with a plasmid containing the GAL2 gene allows these strains to grow on galactose. Initial genetic analyses did not demonstrate linkage between the GAL2 and IMP1 genes owing to the effects of an unlinked gene on the Imp phenotype. By disrupting the GAL2 gene in an Imp+ background, we have shown that IMP1 and GAL2 segregate as tightly linked genes. Based on these data, we believe that imp1 is a partially defective allele of the GAL2 gene.
我们发现，许多酵母实验室菌株由于先前鉴定的核基因IMP1中的隐性突变而在半乳糖代谢方面存在缺陷。这种缺陷导致在半乳糖上生长和代谢需要线粒体功能。遗传背景会影响细胞缺陷的程度。特别是，GAL3的等位基因会影响对Imp表型进行评分的能力。我们发现，在imp1菌株中，半乳糖诱导基因（GAL1、2、7 + 10、MEL1）的转录诱导是正常的，但在rho+和rho0细胞中半乳糖转运均减少。这种表型通常与半乳糖通透酶GAL2中的突变有关。尽管gal2和imp1突变体的生长表型不同，但我们发现用含有GAL2基因的质粒转化imp1 rho0菌株可使这些菌株在半乳糖上生长。由于一个不连锁基因对Imp表型的影响，最初的遗传分析未证明GAL2和IMP1基因之间存在连锁关系。通过在Imp+背景中破坏GAL2基因，我们已表明IMP1和GAL2作为紧密连锁的基因分离。基于这些数据，我们认为imp1是GAL2基因的一个部分缺陷等位基因。
