Mutant

About: Mutant is a research topic. Over the lifetime, 74520 publications have been published within this topic receiving 3477079 citations.

The WHI1+ gene of Saccharomyces cerevisiae tethers cell division to cell size and is a cyclin homolog.

Abstract: WHI1-1 is a dominant mutation that reduces cell volume by allowing cells to commit to division at abnormally small sizes, shortening the G1 phase of the cell cycle. The gene was cloned, and dosage studies indicated that the normal gene activated commitment to division in a dose-dependent manner, and that the mutant gene had a hyperactive but qualitatively similar function. Mild over-expression of the mutant gene eliminated G1 phase, apparently entirely relaxing the normal G1 size control, but revealing hitherto cryptic controls. Sequence analysis showed that the hyperactivity of the mutant was caused by the loss of the C-terminal third of the wild-type protein. This portion of the protein contained PEST regions, which may be signals for protein degradation. The WHI1 protein had sequence similarity to clam cyclin A, to sea urchin cyclin and to Schizosaccharomyces pombe cdc13, a cyclin homolog. Since cyclins are inducers of mitosis, WHI1 may be a direct regulator of commitment to division. A probable accessory function of the WHI1 activator is to assist recovery from alpha factor arrest; WHI1-1 mutant cells could not be permanently arrested by pheromone, consistent with a hyperactivation of division.

Characterization of MexE–MexF–OprN, a positively regulated multidrug efflux system of Pseudomonas aeruginosa

Abstract: Antibiotic-resistant mutants of Pseudomonas aeruginosa were generated using chloramphenicol and ciprofloxacin as selective agents. These mutants displayed a multidrug phenotype and overexpressed an outer membrane protein of 50 kDa, which was shown by Western blot analysis to correspond to OprN. A cosmid clone harbouring the oprN gene was isolated by partial complementation of a mutant deficient in OprM, the outer membrane component of the mexAB-oprM efflux operon. Antibiotic-accumulation studies indicated that OprN was part of an energy-dependent antibiotic-efflux system. Sequencing of a 6180bp fragment from the complementing cosmid revealed the presence of three open reading frames (ORFs), which exhibited amino acid similarity to the components of the mexAB-oprM and mexCD-oprJ efflux operons of P. aeruginosa. The ORFs were designated MexE, MexF and OprN. Mutation of the mexE gene eliminated the multidrug-resistance phenotype in an OprN-overexpressing strain, but did not affect the susceptibility profile of the wild-type strain. Expression of the mexEF-oprN operon was shown to be positively regulated by a protein encoded on a 1.5 kb DNA fragment located upstream of mexE and belonging to the LysR family of transcriptional activators. The presence of a plasmid containing this DNA fragment was sufficient to confer a multidrug phenotype onto the wild-type strain but not onto the mexE mutant. Evidence is provided to show that the mexEF-oprN operon may be involved in the excretion of intermediates for the biosynthesis of pyocyanin, a typical secondary metabolite of P. aeruginosa.

Hepatocytes corrected by gene therapy are selected in vivo in a murine model of hereditary tyrosinaemia type I

Abstract: Current strategies for hepatic gene therapy are either quantitatively inefficient or suffer from lack of permanent gene expression. We have utilized an animal model of hereditary tyrosinaemia type I (HT1), a recessive liver disease caused by deficiency of fumarylacetoacetate hydrolase (FAH), to determine whether in vivo selection of corrected hepatocytes could improve the efficiency of liver gene transfer. As few as 1,000 transplanted wild-type hepatocytes were able to repopulate mutant liver, demonstrating their strong competitive growth advantage. Mutant hepatocytes corrected in situ by retroviral gene transfer were also positively selected. In mutant animals treated by multiple retrovirus injections >90% of hepatocytes became FAH positive and liver function was restored to normal. Our results demonstrate that in vivo selection is a useful strategy for hepatic gene therapy and may lead to effective treatment of human HT1 by retroviral gene transfer.

d14, a strigolactone-insensitive mutant of rice, shows an accelerated outgrowth of tillers.

Abstract: Recent studies using highly branched mutants of pea, Arabidopsis and rice have demonstrated that strigolactones, a group of terpenoid lactones, act as a new hormone class, or its biosynthetic precursors, in inhibiting shoot branching. Here, we provide evidence that DWARF14 (D14) inhibits rice tillering and may act as a new compo-nent of the strigolactone-dependent branching inhibition pathway. The d14 mutant exhibits increased shoot branch-ing with reduced plant height like the previously characterized strigolactone-deficient and -insensitive mutants d10 and d3, respectively. The d10-1 d14-1 double mutant is phenotypically indistinguishable from the d10-1 and d14-1 single mutants, consistent with the idea that D10 and D14 function in the same pathway. However, unlike with d10, the d14 branching phenotype could not be rescued by exogenous strigolactones. In addition, the d14 mutant contained a higher level of 2'-epi-5-deoxystrigol than the wild type. Positional cloning revealed that D14 encodes a protein of the alpha/beta-fold hydrolase superfamily, some members of which play a role in metabolism or signaling of plant hormones. We propose that D14 functions downstream of strigolactone synthesis, as a component of hormone signaling or as an enzyme that participates in the conversion of strigolactones to the bioactive form.

Genetic Control of the Cell-Division Cycle in Yeast, I. Detection of Mutants

Abstract: Time-lapse photomicroscopy has been utilized to detect temperature-sensitive yeast mutants that are defective in gene functions needed at specific stages of the cell-division cycle. This technique provides two types of information about a mutant: the time at which the defective gene function is normally performed, defined as the execution point, and the stage at which cells collect when the function is not performed, defined as the termination point. Mutants carrying lesions in three genes that control the cell-division cycle are described. All three genes, cdc-1, cdc-2, and cdc-3, execute early in the cell cycle at about the time of bud initiation, but differ in their termination points. Cells carrying the cdc-1 mutation terminate at the execution point, most cells ending up with a tiny bud that does not develop further. Cells carrying the cdc-2 mutation terminate at mitosis. Cells carrying the cdc-3 mutation are defective in cell separation but show no definite termination point since other processes of the cell cycle, such as bud initiation and nuclear division, continue despite the block in cell separation.