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S W Liebman

Publications and source records attributed to S W Liebman.

At least 55 records · Page 3Linked to original sources
PubMed1989

Analysis of yeast retrotransposon Ty insertions at the CAN1 locus.

The target site distribution for 55 independent Ty insertions that inactivate the function of the Saccharomyces cerevisiae CAN1 gene is reported. Under some selection conditions Ty elements inserted preferentially into the promoter and exhibited an orientation bias. In contrast, under other conditions no insertions were detected in the promoter region and transposition appeared to occur randomly throughout the CAN1 coding sequence. These results show that the target site distribution for Ty insertions may be a function of the selection conditions.

Base Sequence↗
PubMed1989

Integration of an aberrant retrotransposon in Saccharomyces cerevisiae.

We describe an atypical composite Ty1 element that apparently resulted from the concurrent integration of two complete elements. A portion of the central region of one of these elements was inverted between two long terminal repeats. Inversions of this type have been detected among unintegrated retroviral circles. It now appears that such intermediates can be incorporated into the genome.

Base Sequence↗
PubMed1988

Mitotic recombination within the centromere of a yeast chromosome.

Centromeres are the structural elements of eukaryotic chromosomes that hold sister chromatids together and to which spindle tubules connect during cell division. Centromeres have been shown to suppress meiotic recombination in some systems. In this study yeast strains genetically marked within and flanking a centromere, were used to demonstrate that gene conversion (nonreciprocal recombination) tracts in mitosis can enter into and extend through the centromere.

Alleles↗
PubMed1988

The same configuration of Ty elements promotes different types and frequencies of rearrangements in different yeast strains.

We examined Ty-mediated genomic rearrangements in three related mitotically dividing haploid yeast strains having the same configuration of Ty elements in the CYC1-sup4 interval of chromosome X. Surprisingly, quite different types and frequencies of rearrangements were found in the three strains. In one strain we found only Ty-mediated deletions, which occurred with a frequency of about 1 X 10(-6). Another strain yielded similar deletions, but approximately one-third of these were accompanied by adjacent Ty-mediated inversions. A third strain was found to have an extremely high rate of inversion/reinversion between two of the three Ty elements. This rate was conservatively estimated to be 1.4 +/- 0.2 X 10(-2) per cell per generation, which is at least 2 orders of magnitude higher than previously reported values for Ty-mediated rearrangements. These data provide evidence that local regions of the genome can, in some cases, be much more fluid than had been previously believed.

Chromosome Deletion↗
PubMed1987

Allosuppressors that enhance the efficiency of omnipotent suppressors in Saccharomyces cerevisiae.

Two recessive Mendelian-allosuppressors have been isolated and have been shown to enhance the efficiency of omnipotent suppressors thought to be translational ambiguity mutations. These allosuppressors are unlinked to each other or to the omnipotent suppressors on which they act. They also increase the efficiency of the serine-inserting UAA-suppressor, SUP16. One allosuppressor is allelic or tightly linked to the previously isolated sal2. Another allosuppressor, called sal6, represents a new locus, unlinked to the previously isolated sal1-sal5 that enhance the efficiency of the UAA-suppressors. When present singly in the absence of suppressors or other modifiers the sal2 and sal6 mutations do not have suppressor activity. However, when sal2 and sal6 are combined together in a haploid cell they do suppress weakly. In addition sal2 becomes a weak suppressor in the presence of the [eta +] modifying factor.

Genes, Fungal↗
PubMed1985

The DEL1 mutator gene in Saccharomyces cerevisiae does not act in trans.

DEL1 strains of the yeast Saccharomyces cerevisiae exhibit a high rate of deletions of the three linked genes, CYC1, OSM1, and RAD7. Classical genetic methods showed that DEL1 segregated as a single Mendelian gene closely linked to CYC1. In addition, genetic evidence suggested that DEL1 was both cis- and trans-dominant (Liebman et al. 1979). Molecular analysis of deletions isolated from a haploid DEL1 strain established that deletion formation was mediated by recombination between yeast transposable elements, Ty's (Liebman et al. 1981). We now report the molecular characterization of deletions isolated from diploids in the trans configuration. This analysis reveals that these deletions probably arose in a two-step process involving mitotic recombination followed by Ty-mediated deletion formation in cis.

Chromosome Deletion↗
PubMed1985

Interaction of UAG suppressors and omnipotent suppressors in Saccharomyces cerevisiae.

Haploids bearing the dominant UAG suppressor, SUP7-a, and various alleles of the omnipotent suppressor sup35 were examined. The presence of the UAG suppressor reduced the efficiency of some alleles of sup35, and caused other sup35 alleles to be lethal. A nonclassical interaction of the dominant suppressor tRNA and the ribosome is proposed to explain these observations.

Codon↗
PubMed1985

Deletions extending from a single Ty1 element in Saccharomyces cerevisiae.

Chromosomal rearrangements associated with one Ty1 element in the iso-1-cytochrome c (CYC1) region of Saccharomyces cerevisiae yeast cells were examined. Most of the rearrangements were deletions of the three linked genes, CYC1, OSM1, and RAD7, and resulted from recombination involving the single Ty1 element and a solo delta in the same orientation. These deletions differed by the number of Ty1 elements (zero, one, or two) remaining after deletion and by restriction site heterogeneities associated with these elements. A single Ty1 element remained at the deletion junction point much more frequently than no Ty1. Apparently the Ty1-associated delta element nearer to the solo delta was involved more often in recombination than the more distal Ty1-associated delta element. The restriction site data implicate gene conversion and suggest that site-specific recombination within the deltas, if occurring, is not the only mechanism of delta-delta recombination. Three other rearrangements bore deletions which began at the end of the Ty1 element and extended into regions not bearing Ty1 or delta sequences. Two of these deletions eliminated 7 kilobases of DNA, although they differed by an associated reciprocal translocation. The third involved a deletion of 14.7 kilobases of DNA associated with an overlapping inversion.

Chromosome Deletion↗
PubMed1984

Yeast amber suppressors corresponding to tRNA3Leu genes.

Amber suppressors previously isolated from the yeast Saccharomyces cerevisiae and belonging to the same phenotypic class (Liebman et al., 1976) were assigned to nine different linkage groups named SUP52 through SUP60. One of these suppressors, SUP52, had been shown to cause the insertion of leucine and had been genetically mapped (Liebman et al., 1977). The following additional amber suppressors were mapped: SUP53 maps near the centromere of chromosome III closely linked to leu2; SUP54 maps on chromosome VII, 6 cM distal to trp5; SUP56 maps on chromosome I, 5.4 cM distal to ade1; SUP57 maps on chromosome VI, closely linked to met10; and SUP58 maps on the left arm of chromosome XI, loosely linked to met14. We show by protein analysis that like SUP52, the suppressors SUP53 through SUP56 are leucine-inserters. Furthermore, by hybridization with a cloned tRNA3Leu probe we demonstrate that at least SUP53, SUP54, SUP55 and SUP56 contain mutations in redundant tRNA3Leu genes because they each generate a new XbaI site in a DNA fragment encompassing a tRNA3Leu gene. These new XbaI sites are predicted by the known sequences of tRNA3Leu genes if the CAA anticodon mutates to the amber suppressing anticodon CTA. It is likely that each of the nine suppressors in this phenotypic class contain similar mutations in different tRNA3Leu genes since we find that there are approximately nine unlinked redundant copies of tRNA3Leu genes in haploid strains.

Autoradiography↗
PubMed1980

The RAD52 gene is not required for the function of the DEL1 mutator gene in Saccharomyces cerevisiae.

The DEL1 mutator inb Saccharomyces cerevisiae leads to the formation of deletions adjacent to itself (Liebman et al. 1979). Here we show that the frequency of these DEL1-promoted deletions is not altered by the presence of the recombination-deficient mutation, rad52-l. This indicates that generalized recombination is not required for the formation of deletions in DEL1 yeast strains.

Chromosome Deletion↗
PubMed1980

An antisuppressor that acts on omnipotent suppressors in yeast.

Six partially dominant antisuppressors were obtained that reduce the efficiency of two omnipotent yeast suppressors, sup45 and sup35, thought to be ribosomal ambiguity mutations. Each of these six antisuppressors was shown to fall within a single Mendelian locus, named asu9. The asu9 mutations are specific for omnipotent suppressors; they have no effect on several dominant tRNA-like suppressors. In the absence of suppressors, asu9 causes sensitivity to the aminoglycoside antibiotic, paromomycin. The properties of asu9 are consistent with the hypothesis that asu9 alters yeast ribosomal proteins.

Chromosome Mapping↗
PubMed1979

A mutator affecting the region of the iso-1-cytochrome c gene in yeast.

The mutator gene DEL1 in the yeast Saccharomyces cerevisiae causes a high rate of formation of multisite mutations that encompass the following three adjacent genes: CYC1, which determines the structure of iso-1-cytochrome c; RAD7, which controls UV sensitivity; and OSM1, which controls osomotic sensitivity. The simplest hypothesis is that these multisite mutations are deletions, although it has not been excluded that they may involve other types of gross chromosomal aberrations. In contrast, normal strains do not produce such multisite mutations even after mutagenic treatments. The multisite mutations arise at a rate of approximately 10(-5) to 10(-6) per cell per division in DEL1 strains, which is much higher than rates observed for mutation of genes in normal strains. For example, normal strains produce all types of cyc1 mutants at a low rate of approximately 10(-8) to 10(-9). No evidence for multisite mutations was obtained upon analysis of numerous spontaneous ade1, ade2, met2 and met15 mutants isolated in a DEL1 strain. DEL1 appears to be both cis- and trans-dominant. The location of the DEL1 gene and the lack of effect on other genes suggest that the mutator acts only on a region adjacent to itself.

Chromosome Aberrations↗
PubMed1979

Extrachromosomal psi+ determinant suppresses nonsense mutations in yeast.

The extrachromosomal psi+ determinant in the yeast Saccharomyces cerevisiae enhanced the expression of Mendelian UAA suppressors by 6- to 10-fold. The psi+ determinant by itself is a weak UAA suppressor that caused the production of approximately 1% of the normal level of iso-1-cytochrome c in a strain containing the UAA mutation cycl-72.

Cytochrome c Group↗
PubMed1976

Inhibition of growth by amber suppressors in yeast.

Strains of the yeast Saccharomyces cerevisiae that contain highly efficient amber (UAG) suppressors grow poorly on nutrient medium, while normal or nearly normal growth rates are observed when these strains lose the supressors or when the suppressors are mutated to lower efficiencies. The different growth rates account for the accumulation of mutants with lowered efficiencies in cultures of strains with highly efficient amber suppressors. Genetic analyses indicate that one of the mutations with a lowered efficiency of suppression is caused by an intragenic mutation of the amber supressor. The inhibition of growth caused by excessive suppression is expected to be exacerbated when appropriate suppressors are combined together in haploid cells if two suppressors act with a greater efficiency than a single suppressor. Such retardation of growth is observed with combinations of two UAA (ochre) suppressors (Gilmore 1967) and with combinations of two UAG suppressors when the efficiencies of each of the suppressors are within a critical range. In contrast, combinations of a UAA suppressor and a UAG suppressor do not affect growth rate. Apparently while either excessive UAA or excessive UAG suppression is deleterious to yeast, a moderate level of simultaneous UAA and UAG suppression is not.

Cytochrome c Group↗
PubMed1976

Isolation and characterization of amber suppressors in yeast.

Nonsense suppressors were obtained in a haploid yeast strain containing eight nutritional mutations, that are assumed to be amber or ochre, and the cyc1-179 amber mutation that has a UAG codon corresponding to position 9 in iso-1-cytochrome c. Previous studies established that the biosynthesis and function of iso-1-cytochrome c is compatible with replacements at position 9 of amino acids having widely different structures (Stewart and Sherman 1972). UV-induced revertants, selected on media requiring the reversion of one or two of the amber nutritional markers, were presumed to contain a suppressor if there was the unselected reversion of at least one other marker. The 1088 suppressors that were isolated could be divided into 78 phenotypic classes. Only 43 suppressors of three classes caused the production of more than 50% of the normal amount of iso-1-cytochrome c in the cyc1-179 strain. Genetic analyses indicated that all of these highly efficient amber suppressors are allelic to one or another of the eight suppressors which cause the insertion of tyrosine at ochre (UAA) codons (Gilmore, Stewart and Sherman 1971). Furthermore, only tyrosine has been identified at position 9 in iso-1-cytochrome c in cyc1-179 strains suppressed with these efficient amber suppressors.

Cytochrome c Group↗