bluuebunny/crossref_metadata_2025_split huggingface dataset:
Female sterile mutations on the second chromosome of Drosophila melanogaster. II. Mutations blocking oogenesis or altering egg morphology.
Authors: Schüpbach T , Wieschaus E 
Published: January 2021

Abstract
In mutagenesis screens for recessive female sterile mutations on the second chromosome of Drosophila melanogaster 528 lines were isolated which allow the homozygous females to survive but cause sterility. In 62 of these lines early stages of oogenesis are affected, and these females usually do not lay any eggs. In 333 lines oogenesis proceeds apparently normally to stage 8 of oogenesis, but morphological defects become often apparent during later stages of oogenesis, and are visible in the defective eggs produced by these females whereas 133 lay eggs that appear morphologically normal, but do not support normal embryonic development. Of the lines 341 have been genetically characterized and define a total of 140 loci on the second chromosome. Not all the loci are specific for oogenesis. From the numbers obtained we estimate that the second chromosome of Drosophila contains about 13 loci that are relatively specific for early oogenesis, 70 loci that are specifically required in mid to late oogenesis, and around 30 maternal-effect lethals.
Splicing of retrotransposon insertions from transcripts of the Drosophila melanogaster vermilion gene in a revertant.
Authors: Pret A M , Searles L L 
Published: January 2021

Abstract
A mutation of the Drosophila melanogaster vermilion (v) gene known as v1 is caused by the insertion of a 412 retrotransposon into the 5' untranslated region of the first exon. Mutants carrying this insertion accumulate a low level of mRNA from which most of the transposon sequences have been eliminated by splicing at cryptic sites within transposon sequences. Here, we demonstrate that a revertant of the v1 allele called v+37 is caused by the insertion of a second retrotransposon, the B104/roo element, into a site near one end of the 412 element. The revertant strain accumulates a higher level of mRNA from which most of both transposons have been removed by splicing at new donor sites introduced by the B104/roo insertion and the same acceptor site within 412. Mutations at suppressor of sable [su(s)], which increase the accumulation of v1 transcripts, slightly elevate the level of v+37 RNA. In addition, we show that the first v intron downstream of the 412 insertion is not efficiently removed in the v1 mutant, and suppressor and reversion mutations increase the proportion of transcripts that are properly spliced at that downstream intron. Thus, it appears that both the suppressor and reversion mutations exert an effect at the level of pre-mRNA splicing.
Molecular population genetics of the distal portion of the X chromosome in Drosophila: evidence for genetic hitchhiking of the yellow-achaete region.
Authors: Begun D J , Aquadro C F 
Published: January 2021

Abstract
We have estimated DNA sequence variation and differentiation within and between Drosophila melanogaster and its sibling species, Drosophila simulans, using six-cutter restriction site variation at yellow-achaete (y-ac), phosphogluconate dehydrogenase (Pgd), and period (per). These three gene regions are of varying distance from the telomere of the X chromosome and range from very low to moderate rates of recombination in D. melanogaster. According to Tajima's test of neutrality, the Pgd region has been influenced by balancing selection in D. melanogaster. This is consistent with previous data suggesting the allozyme polymorphism at this locus is visible to selection. The Hudson, Kreitman, Aguadé test of neutrality reveals a significant departure from neutrality for the y-ac region compared to the per or rosy regions in D. simulans. There is also a significant departure for the y-ac region compared to the Adh 5' flanking region in D. melanogaster. In both species the departure appears to be due to reduced variation at y-ac compared to that expected from divergence between D. simulans and D. melanogaster. We conclude that recent hitchhiking associated with the selective fixation of one or more advantageous mutants in the y-ac region is the best explanation for reduced variation at y-ac.
Specificity of base substitutions induced by the acridine mutagen ICR-191: mispairing by guanine N7 adducts as a mutagenic mechanism.
Authors: Sahasrabudhe S R , Luo X , Humayun M Z 
Published: January 2021

Abstract
As the most nucleophilic site in DNA, the guanine N7 atom is a major site of adduction by a large number of alkylating mutagens and carcinogens. Aflatoxin B1, a powerful mutagen, is believed to act through its reaction with this DNA site. On the basis of the specificity of base substitutions induced by various adduct forms of aflatoxin, we have proposed that bulky guanine N7 adducts elicit base substitutions by two mechanisms. The first mechanism is similar to that observed for a number of bulky noninstructive lesions, whereas the second mechanism invokes mispairing between N7-adducted guanine and thymine. A prediction of the mispairing hypothesis is that diverse bulky guanine N7 adducts (regardless of structural similarities with the aflatoxins) should induce predominantly G-to-A transitions. Accordingly, we have recently observed that base substitutions induced by the acridine half-mustard ICR-191 in the M13 double-stranded DNA transfection system are predominantly G:C-to-A:T transitions. Here, by transfecting ICR-191-treated M13 AB28 single-stranded DNA into Escherichia coli, we show that base substitutions are predominantly targeted to guanines. Since the N7-adducted-guanine:thymine mispairing is proposed to require N1 deprotonation promoted by the primary N7 lesion, guanine imidazole ring-opening should abolish this mispairing property, and thereby alter the specificity of mutagenesis. Here, we show that the incubation of ICR-191-treated RF DNA at pH 10.5 results in a significant reversal of the specificity of G:C-targeted substitutions such that G-to-T transversions predominated over G-to-A transitions.(ABSTRACT TRUNCATED AT 250 WORDS)
The theoretical distribution of lengths of intact chromosome segments around a locus held heterozygous with backcrossing in a diploid species.
Authors: Naveira H , Barbadilla A 
Published: January 2021

Abstract
When two different isogenic lines of a diploid species (or two different species) are crossed, the resulting F1 individuals should be heterozygous at all the loci fixed for different alleles in the two strains (in the limit, at all the loci of the genome). If one of these loci is then held heterozygous for several generations of repeated backcrossing to the same strain, the average length of intact chromosome segments (with reference to the original parental chromosome) on both sides of the selected locus, or, equivalently, the average length of segments surrounding that locus which are still heterozygous (with reference to the fully heterozygous F1 chromosome), may diminish, but cannot increase. Several authors have derived equations to predict this average. We show that the most widely used criterion, developed by R.A. Fisher, leads to serious overestimations of the true parametric values, when applied to early generation analyses, with the corresponding errors in the interpretation of experimental results. We then derive the exact equations both for the average and standard deviation of the lengths of intact chromosome segments surrounding a locus held heterozygous after any number of generations of backcrossing. Our results are in close agreement with those found by a former author, although involving a rather different approach.
The maintenance of single-locus polymorphism. IV. Models with mutation from existing alleles.
Authors: Spencer H G , Marks R W 
Published: January 2021

Abstract
The ability of viability selection to maintain allelic polymorphism is investigated using a constructionist approach. In extensions to the models we have previously proposed, a population is bombarded with a series of mutations whose fitnesses in conjunction with other alleles are functions of the corresponding fitnesses with a particular allele, the parent allele, already in the population. Allele frequencies are iterated simultaneously, thus allowing alleles to be driven to extinction by selection. Such models allow very high levels of polymorphism to evolve: up to 38 alleles in one case. Alleles that are lethal as homozygotes can evolve to surprisingly high frequencies. The joint evolution of allele frequencies and viabilities highlights the necessity to consider more than the current morphology of a population. Comparisons are made with the neutral theory of evolution and it is suggested that failure to reject neutrality using the Ewens-Watterson test cannot be regarded as evidence for the neutral theory.
Promoters of the broad host range plasmid RK2: analysis of transcription (initiation) in five species of gram-negative bacteria.
Authors: Greener A , Lehman S M , Helinski D R 
Published: January 2021

Abstract
A broad host range cloning vector was constructed, suitable for monitoring promoter activity in diverse Gram-negative bacteria. This vector, derived from plasmid RSF1010, utilized the firefly luciferase gene as the reporter, since the assay for its bioluminescent product is sensitive, and measurements can be made without background from the host. Twelve DNA fragments with promoter activity were obtained from broad host range plasmid RK2 and inserted into the RSF1010 derived vector. The relative luciferase activities were determined for these fragments in five species of Gram-negative bacteria. In addition, four promoters were analyzed by primer extension to locate transcriptional start sites in each host. The results show that several of the promoters vary substantially in relative strengths or utilize different transcriptional start sites in different bacteria. Other promoters exhibited similar activities and identical start sites in the five hosts examined.
A cytogenetic and genetic characterization of a group of closely linked second chromosome mutations that suppress position-effect variegation in Drosophila melanogaster.
Authors: Sinclair D A , Ruddell A A , Brock J K , Clegg N J , Lloyd V K , Grigliatti T A 
Published: January 2021

Abstract
Characterization of a group of dominant second chromosome suppressor of position-effect variegation (PEV) (Su(var)) mutants has revealed a variety of interesting properties, including: maternal-effect suppression of PEV, homozygous lethality or semilethality and male-specific hemizygous lethality, female infecundity, acute sensitivity to the amount of heterochromatin in the cell and sensitivity to sodium butyrate. Deficiency/duplication mapping and complementation tests have revealed that eight of the mutants define at least two genes in section 31 of the left arm of chromosome 2 and they suggest that a ninth corresponds to an additional nonessential Su(var) gene within or near this region. The effects of specific deficiencies and a duplication on PEV indicate that the expression of one or more of the Su(var) genes in this region of the chromosome is dose-dependent, i.e., capable of haplo-abnormal suppression and triplo-abnormal enhancement. Interestingly, the appearance of certain visible phenotypes among a subset of the mutants suggests that they may possess antimorphic properties. Our results are consistent with the hypothesis that two of these Su(var) genes encode structural components of heterochromatin. We also report that two previously isolated mutants located in 31E and 31F-32A act as recessive suppressors of PEV.
Site-specific recombination determined by I-SceI, a mitochondrial group I intron-encoded endonuclease expressed in the yeast nucleus.
Authors: Plessis A , Perrin A , Haber J E , Dujon B 
Published: January 2021

Abstract
The Saccharomyces cerevisiae mitochondrial endonuclease I-SceI creates a double-strand break as the initiating step in the gene conversional transfer of the omega+ intron to omega- DNA. We have expressed a galactose-inducible synthetic I-SceI gene in the nucleus of yeast that also carries the I-SceI recognition site on a plasmid substrate. We find that the galactose-induced I-SceI protein can be active in the nucleus and efficiently catalyze recombination. With a target plasmid containing direct repeats of the Escherichia coli lacZ gene, one copy of which is interrupted by a 24-bp cutting site, galactose induction produces both deletions and gene conversions. Both the kinetics and the proportion of deletions and gene conversions are very similar to analogous events initiated by a galactose-inducible HO endonuclease gene. We also find that, in a rad52 mutant strain, the repair of double-strand breaks initiated by I-SceI and by HO are similarly affected: the formation of deletions is reduced, but not eliminated. Altogether, these results suggest either that the two endonucleases act in the same way after double-strand break formation or that the two endonucleases are not involved in subsequent steps.
Molecular organization of the X chromosome in different species of the obscura group of Drosophila.
Authors: Segarra C , Aguadé M 
Published: January 2021

Abstract
Nine single copy regions located on the X chromosome have been mapped by in situ hybridization in six species of the obscura group of Drosophila. Three Palearctic species, D. subobscura, D. madeirensis and D. guanche, and three Nearctic species, D. pseudoobscura, D. persimilis and D. miranda, have been studied. Eight of the regions include known genes from D. melanogaster (Pgd, zeste, white, cut, vermilion, RNA polymerase II 215, forked and suppressor of forked) and the ninth region (lambda DsubF6) has not yet been characterized. In all six species, as in D. melanogaster, all probes hybridize to a single site. Established chromosomal arm homologies of Muller's element A are only partly supported by present results since two of the probes (Pgd and zeste) hybridize at the proximal end of the XR chromosomal arm in the three Nearctic species. In addition to the centric fusion of Muller's A (= XL) and D (= XR) elements, the metacentric X chromosome of the Nearctic species requires a pericentric inversion to account for this result. Previously proposed homologies of particular chromosomal regions of the A (= X) chromosome in the three species of the D. subobscura cluster and of the XL chromosomal arm in the three species of the D. pseudoobscura cluster are discussed in light of the present results. Location of the studied markers has changed drastically not only since the divergence between the melanogaster and obscura groups but also since the Palearctic and Nearctic species of the obscura group diverged.
Tandem repeats in extrachromosomal ribosomal DNA of Dictyostelium discoideum, resulting from chromosomal mutations.
Authors: Cole R A , Williams K L 
Published: January 2021

Abstract
Extrachromosomal ribosomal DNA in the simple eukaryote Dictyostelium discoideum is readily separated from chromosomal DNA by orthogonal field electrophoresis (OFAGE), forming a prominent band in the 110-kb region of the gel. Here we show that mutations in at least two chromosomal genes give rise to a ladder of rDNA bands increasing in size up to about 300 kb. One of these mutations, the rrcA350 allele, which is recessive to wild type and maps to the centromere-proximal region of linkage group II, has an unstable phenotype; spontaneous revertants, which no longer exhibit the rDNA ladder, have been recovered. Another mutation rrc-351, provisionally mapped to linkage group IV, is dominant to wild type. The rDNA ladder is caused by concatamerization of a 34-kb fragment in the nontranscribed central spacer region of the 88-kb linear rDNA palindrome. Restriction enzyme analysis has revealed that each concatamer is generated by crossovers between two rDNA molecules.
COTRANS: a program for cotransduction analysis.
Authors: Berlyn M B , Letovsky S 
Published: January 2021

Abstract
COTRANS is a program for analyzing cotransduction data. It calculates distances from pairwise cotransduction frequencies, computes crossovers required to obtain each observed recombinant class, and applies rules to draw conclusions about order. The rules are based on the correlation between the frequency of the classes and the number of required crossovers for each possible ordering compatible with the distance calculations. The procedure emulates a geneticist's stepwise analysis of the data by first calculating distances, then looking for obvious three-point ordering conclusions, and finally proceeding to a complete crossover analysis. It reports results from each step of the analysis and an overall conclusion. COTRANS provides significant gains in speed and convenience over hand analysis, particularly for multipoint crosses with several recombinant classes.
Selection for early meiotic mutants in yeast.
Authors: Mitchell A P , Bowdish K S 
Published: January 2021

Abstract
In the yeast Saccharomyces cerevisiae, only a/alpha cells can enter meiosis; a and alpha cells cannot. Because a/alpha cells are typically diploid and a and alpha cells are typically haploid, this cell type restriction ensures that only diploid cells enter meiosis. Entry into meiosis is accompanied by an increase in expression of the IME1 gene; the IME1 product (IME1) then activates IME2 and other meiotic genes. We have found that IME1 expression is toxic to starved haploid cells, presumably because IME1 directs them into meiosis. IME1 toxicity is greater in rad52 mutants, in which meiotic recombination causes lethal damage. Suppressors of IME1 toxicity include recessive mutations in two genes, RIM11 and RIM16 (Regulator of Inducer of Meiosis), that are required for IME1 to activate IME2 expression. RIM11 maps near CIN4 on chromosome XIII.
Genetic recombination in bacteriophage T4: single-burst analysis of cosegregants and evidence in favor of a splice/patch coupling model.
Authors: Shcherbakov V P , Plugina L A , Nesheva M A 
Published: January 2021

Abstract
To reveal the structure of penultimate DNA intermediates in T4 bacteriophage recombination, resolution of which produces free recombinant molecules, a single-burst analysis of the recombinant progeny was made in multifactor crosses, enabling one to determine quantitatively the different recombinants generated by one or two exchanges within the same chromosome segment. It was found that double and single exchanges are highly correlated in T4 recombination. These results were interpreted as evidence for simultaneous formation of a splice/patch pair as the primary recombination products. A recombination model called here the "splice/patch coupling model" is presented according to which resolution of a single DNA intermediate results in two linear heterozygous molecules containing a patch and a splice, respectively, in homologous positions.
Isolation and characterization of SUA5, a novel gene required for normal growth in Saccharomyces cerevisiae.
Authors: Na J G , Pinto I , Hampsey M 
Published: January 2021

Abstract
We have identified the sua5 locus as a suppressor of an aberrant ATG codon located in the leader region of the cyc1 gene. The sua5-1 allele enhances the iso-1-cytochrome c steady state level in the cyc1-1019 mutant from 2% to approximately 60% of normal (Cyc+) and also confers a marked slow growth (Slg-) phenotype. Suppression is not a consequence of altered transcription initiation at the cyc1 locus. The SUA5 wild-type gene was isolated and sequenced, revealing an open reading frame (ORF) encoding a potential protein of 46,537 Da. SUA5 transcript analyses were consistent with expression of the predicted ORF and Sua5 antisera detected a protein with an apparent molecular mass of 44 kDa. SUA5 was mapped to chromosome VII, immediately adjacent to the PMR1 gene. Hybridization analysis revealed the presence of a related gene on chromosome XII. Neither the SUA5 DNA sequence nor deduced amino acid sequence showed homology to any sequences in the data banks. Disruption of SUA5 conferred the same Cyc+ and Slg- phenotypes as the sua5-1 suppressor, which is the result of a missense mutation, encoding a Ser107----Phe replacement. In addition, sua5 null mutants lack cytochrome a.a3 and fail to grow on lactate or glycerol medium. These results define SUA5 as a new gene encoding a novel protein that is necessary for normal cell growth.
Variable rates of evolution among Drosophila opsin genes.
Authors: Carulli J P , Hartl D L 
Published: January 2021

Abstract
DNA sequences and chromosomal locations of four Drosophila pseudoobscura opsin genes were compared with those from Drosophila melanogaster, to determine factors that influence the evolution of multigene families. Although the opsin proteins perform the same primary functions, the comparisons reveal a wide range of evolutionary rates. Amino acid identities for the opsins range from 90% for Rh2 to more than 95% for Rh1 and Rh4. Variation in the rate of synonymous site substitution is especially striking: the major opsin, encoded by the Rh1 locus, differs at only 26.1% of synonymous sites between D. pseudoobscura and D. melanogaster, while the other opsin loci differ by as much as 39.2% at synonymous sites. Rh3 and Rh4 have similar levels of synonymous nucleotide substitution but significantly different amounts of amino acid replacement. This decoupling of nucleotide substitution and amino acid replacement suggests that different selective pressures are acting on these similar genes. There is significant heterogeneity in base composition and codon usage bias among the opsin genes in both species, but there are no consistent relationships between these factors and the rate of evolution of the opsins. In addition to exhibiting variation in evolutionary rates, the opsin loci in these species reveal rearrangements of chromosome elements.
Molecular genetic studies of the Cdc7 protein kinase and induced mutagenesis in yeast.
Authors: Hollingsworth R E , Ostroff R M , Klein M B , Niswander L A , Sclafani R A 
Published: January 2021

Abstract
The Saccharomyces cerevisiae CDC7 gene encodes a protein kinase that functions in DNA replication, repair, and meiotic recombination. The sequence of several temperature-sensitive (ts) cdc7 mutations was determined and correlated with protein kinase consensus domain structure. The positions of these ts alleles suggests some general principles for predicting ts protein kinase mutations. Pedigree segregation lag analysis demonstrated that all of the mutant proteins are less active or less stable than wild-type Cdc7p. Two new mutations were constructed, one by site-directed and the other by insertional mutagenesis. All of the cdc7 mutants were assayed for induced mutagenesis in response to mutagenic agents at the permissive temperature. Some cdc7 mutants were found to be hypomutable, while others are hypermutable. The differences in mutability are observed most clearly when log phase cells are used. Both hypo- and hypermutability are recessive to wild type. Cdc7p may participate in DNA repair by phosphorylating repair enzymes or by altering chromatin structure to allow accessibility to DNA lesions.