bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of novel pentose transporters in Kluyveromyces marxianus using a new screening platform
Authors: Donzella Lorena , Varela Javier A , Sousa Maria João , Morrissey John P
Published: April 2021

The capacity of yeasts to assimilate xylose or arabinose is strongly dependent on plasma membrane transport proteins. Because pentoses comprise a substantial proportion of available sugars in lignocellulosic hydrolysates, their utilisation is centrally important for the development of second generation biorefineries. Relatively few native pentose transporters have been studied and there is intense interest in expanding the repertoire. To aid the identification of novel transporters, we developed a screening platform in the native pentose-utilising yeast Kluyveromyces marxianus. This involved the targeted deletion of twelve transporters of the major facilitator superfamily (MFS) and application of a synthetic biology pipeline for rapid testing of candidate pentose transporters. Using this K. marxianus ΔPT platform, we identified several K. marxianus putative xylose or arabinose transporter proteins that recovered a null strain's ability to growth on these pentoses. Four proteins of the HGT-family were able to support growth in media with high or low concentrations of either xylose or arabinose, while six HXT-like proteins displayed growth only at high xylose concentrations, indicating solely low affinity transport activity. The study offers new insights into the evolution of sugar transporters in yeast and expands the set of native pentose transporters for future functional and biotechnological studies.
Drinking, eating and dancing: Swiss merchants’ lobbying in seventeenth- and eighteenth-century Lyon
Authors: Schnyder Marco
Published: April 2021

At the beginning of the eighteenth century, the Swiss formed the most important and numerous foreign merchant community in Lyon. As a result of centuries-old treaties, Swiss nationals benefited from several privileges in France. However, these privileges were increasingly threatened by French protectionist policies. In order to defend their rights, Swiss merchants adopted various strategies. In this article, the focus is on a particular form of lobbying: dinners and parties. The merchants themselves documented such events in their own writings. In general terms these sources offer an original research perspective on early modern urban food, drinking and ceremonial culture. More specifically, this article reveals not only the different facets of a foreign community’s agency in a protectionist context, but it also contributes to a better understanding of the internal relations within this merchant community, such as between its Protestant and Catholic members.
Mutation Rates and Selection on Synonymous Mutations in SARS-CoV-2
Authors: De Maio Nicola , Walker Conor R , Turakhia Yatish , Lanfear Robert , Corbett-Detig Russell , Goldman Nick
Published: April 2021

The COVID-19 pandemic has seen an unprecedented response from the sequencing community. Leveraging the sequence data from more than 140,000 SARS-CoV-2 genomes, we study mutation rates and selective pressures affecting the virus. Understanding the processes and effects of mutation and selection has profound implications for the study of viral evolution, for vaccine design, and for the tracking of viral spread. We highlight and address some common genome sequence analysis pitfalls that can lead to inaccurate inference of mutation rates and selection, such as ignoring skews in the genetic code, not accounting for recurrent mutations, and assuming evolutionary equilibrium. We find that two particular mutation rates, G →U and C →U, are similarly elevated and considerably higher than all other mutation rates, causing the majority of mutations in the SARS-CoV-2 genome, and are possibly the result of APOBEC and ROS activity. These mutations also tend to occur many times at the same genome positions along the global SARS-CoV-2 phylogeny (i.e., they are very homoplasic). We observe an effect of genomic context on mutation rates, but the effect of the context is overall limited. Although previous studies have suggested selection acting to decrease U content at synonymous sites, we bring forward evidence suggesting the opposite.
ALTERED MAIZE ENDOSPERM ADP-GLUCOSE PYROPHOSPHORYLASES FROM REVERTANTS OF A SHRUNKEN-2-DISSOCIATION ALLELE
Authors: Tuschall D M , Hannah L C
Published: April 2021

Four phenotypically wild-type seeds were obtained from separate Activator-induced events in the Dissociation-inhibited allele sh2-ml (shrunken-2, mutable-1). Endosperm adenosine diphosphoglucose pyrophosphorylase, the enzyme controlled by sh2, was extracted and partially purified from the four revertants and was compared to enzyme produced by the progenitor Sh2 allele and the sh2-m allele.

The revertants contained 50 to 140% of the activity conditioned by the progenitor allele. Each of the revertants appears to be unique as judged by differences in Km(glucose-1-PO4), 3-phosphoglycerate(3-PGA) activation, and phosphate-inhibition. In one case the reversion event apparently increased the sensitivity of ADP-glucose pyrophosphorylate to 3-PGA activation.
[HOK], A NEW YEAST NON-MENDELIAN TRAIT, ENABLES A REPLICATION-DEFECTIVE KILLER PLASMID TO BE MAINTAINED
Authors: Wickner Reed B , Toh-E Akio
Published: April 2021

The K1 killer plasmid, [KIL-k1], of Saccharomyces cerevisiae is a 1.25 × 106 dalton linear double-stranded RNA plasmid coding for a protein toxin and immunity to that toxin. The [KIL-sd1] plasmid is a replication-defective mutant of [KIL-k1] that depends on one of the recessive chromosomal superkiller (ski  -) mutations for its maintenance (Toh-e and Wickner 1979). This report concerns a means by which [KIL-sd1] can be stably maintained in a SKI  + host. Strains carrying a plasmid we call [HOK] (helper of killer) stably maintain [KIL-sd1]. [HOK] segregates 4 [HOK]:0 in meiotic crosses and is efficiently transferred by cytoplasmic mixing (heterokaryon formation). [HOK] depends for its maintenance on the products of PET18, MAK3, and MAK10, three chromosomal genes needed to maintain [KIL-k1], but is independent of 10 other MAK genes and of MKT1. [HOK] is not mitochondrial DNA and is unaffected by agents which convert ψ+ strains to ψ-. [HOK] is also distinct from the previously described plasmids [URE3], 20S RNA, 2 µ DNA, and [EXL]. Strains lacking [HOK] consistently have a four-fold lower copy number of L double-stranded RNA than strains carrying [HOK].
FORMATION OF F'TRP PLASMIDS IN ESCHERICHIA COLI K12
Authors: Van Gijsegem Frédérique , Toussaint Ariane
Published: April 2021

From strains carrying two different F-prime factors, we recovered F′ derivatives that acquired the trp chromosomal region. These F′trp plasmids can be isolated at a frequency of 10-5 to 10-6. They were characterized genetically by looking at the size of the trp segment they acquired and at the location of that segment in the parental F′ plasmid. Results are discussed in relationship to possible transposition mechanisms.
EFFECT OF RADIATION DOSAGE ON EFFICIENCY OF CHLOROPLAST TRANSFER BY PROTOPLAST FUSION IN NICOTIANA
Authors: Menczel László , Galiba Gábor , Nagy Ferenc , Maliga Pál
Published: April 2021

Chloroplasts of Nicotiana tabacum SR1 were transferred into Nicotiana plumbaginifolia by protoplast fusion. The protoplasts of the organelle donor were irradiated with different lethal doses using a 60Co source, to facilitate the elimination of their nuclei from the fusion products. After fusion induction, clones derived from fusion products and containing streptomycin-resistant N. tabacum SR1 chloroplasts were selected by their ability to green on a selective medium. When N. tabacum protoplasts were inactivated by iodoacetate instead of irradiation, the proportion of N. plumbaginifolia nuclear segregant clones was low (1-2%). Irradiation markedly increased this value: Using 50, 120, 210 and 300 J kg-1 doses, the frequency of segregant clones was 44, 57, 84 and 70 percent, respectively. Regeneration of resistant N. plumbaginifolia plants with SR1 chloroplasts indicated that plastids can be rescued from the irradiated cells by fusion with untreated protoplasts. Resistant N. plumbaginifolia plants that were regenerated (43 clones studied) had diploid (2n = 2X = 20) or tetraploid chromosome numbers and were identical morphologically to parental plants. The absence of aneuploids suggests that in these clones irradiation resulted in complete elimination of the irradiated N. tabacum nuclei. Resistance is inherited maternally (five clones tested). The demonstration of chloroplast transfer and the presence of N. tabacum plastids in the N. plumbaginifolia plants was confirmed by chloroplast DNA fragmentation patterns after EcoRI digestion.
FREQUENCIES OF NULL ALLELES AT ENZYME LOCI IN NATURAL POPULATIONS OF PONDEROSA AND RED PINE
Authors: Allendorf Fred W , Knudsen Kathy L , Blake George M
Published: April 2021

Pinus ponderosa and P. resinosa population samples have mean frequencies of enzymatically inactive alleles of 0.0031 and 0.0028 at 29 and 27 enzyme loci, respectively. Such alleles are rare and are apparently maintained by selection-mutation balance. Ponderosa pine have much higher amounts of allozymic and polygenic phenotypic variation than red pine, yet both species have similar frequencies of null alleles. Thus, null alleles apparently do not contribute to polygenic variation, as has been suggested. The concordance between allozymic and polygenic variation adds support to the view that allozyme studies may be valuable in predicting the relative amount of polygenic variation in populations.
THE MATHEMATICS OF MOSAIC ANALYSIS III. ANALYSIS OF STRUCTURES WITH EXTENT IN TWO DIMENSIONS
Authors: Wyman Robert J , Costello Walter J , Koto Mary L
Published: April 2021

This paper derives formulae for the use of mosaic analysis to determine the sizes, shapes and locations of structures that are not points but are extended areas on the blastoderm. We consider a male patch of any convex shape and size and a structure of any convex shape and size. The probability that these two intersect in a set of mosaics is simply one-quarter the product of their perimeters. From this perimeter formula we derive equations relating the frequency of mosaicism of a structure to its size and we derive a formula for the mapping of lethal foci. We then develop a method to locate the borders of a focus that covers an area on the blastoderm.
EVOLUTION OF A REGULATED OPERON IN THE LABORATORY
Authors: Hall Barry G
Published: April 2021

The evolution of new metabolic functions is being studied in the laboratory using the EBG system of E. coli as a model system. It is demonstrated that the evolution of lactose utilization by lacZ deletion strains requires a series of structural and regulatory gene mutations. Two structural gene mutations act to increase the activity of ebg enzyme toward lactose, and to permit ebg enzyme to convert lactose into allolactose, an inducer of the lac operon. A regulatory mutation increases the sensitivity of the ebg repressor to lactose, and permits sufficient ebg enzyme activity for growth. The resulting fully evolved ebg operon regulates its own expression, and also regulates the synthesis of the lactose permease.
THE GENETICS OF A SMALL AUTOSOMAL REGION OF DROSOPHILA MELANOGASTER CONTAINING THE STRUCTURAL GENE FOR ALCOHOL DEHYDROGENASE. III. HYPOMORPHIC AND HYPERMORPHIC MUTATIONS AFFECTING THE EXPRESSION OF HAIRLESS
Authors: Ashburner Michael
Published: April 2021

A lethal locus (1(2)br7;35B6-10), near Adh on chromosome arm 2L of D. melanogaster, is identified with Plunkett's dominant suppressor of Hairless (H). Of eight new alleles, seven act as dominant suppressors of H, the eighth is a dominant enhancer of H. One of the suppressor alleles is both a leaky lethal and a weak suppressor of H. Confirming Nash (1970), deletions of 1(2)br7 are dominant suppressors, and duplications are dominant enhancers of H. A simple model is proposed to account for the interaction of 1(2)br7 and H, assuming that amorphic (or hypomorphic) alleles of l(2)br7 suppress H and that hypermorphic alleles enhance H.
Recombination and replication of plasmid-like derivatives of a short section of the mitochondrial chromosome of Neurospora crassa.
Authors: Gross S R , Levine P H , Metzger S , Glaser G
Published: April 2021

The 21-kbp mitochondrial chromosome of the stp-ruv strain of Neurospora crassa undergoes regional amplification yielding plasmid-like supercoiled circles varying in size from subunit length to very high multimers. A comparison of the base sequence of the five plasmids studied, with the region of the chromosome from which they were derived, indicated that the amplified chromosomal segments were determined by a recombination-excision process near or within two structurally distinctive regions. One of these, consisting of nearly uninterrupted strings of Cs and Gs straddling tandem PstI site direct repeats, could form an extended hairpin loop with only a few mismatches. It was found at or near the 5' exchange point of all of the plasmids. An extended 35-bp sequence containing 17-bp direct repeats was the primary 3' site of exchange. Base sequence changes were found in the vicinity of exchange points. Most notable of these was a G insertion and T to C transition within a section of the 5' region likely to form a hairpin loop, suggesting the involvement of a mismatch repair-like mechanism in the recombination process. The sequence, TATATAGACATATA, was identified as a likely candidate for the site of replication initiation. A nearly identical sequence was found common to all of the corresponding plasmids of Podospora anserina and was reported near the presumed replication origin of the Drosophila yakuba mitochondrial chromosome. A search of GenBank revealed a remarkable association of the consensus sequence, TATATAGAXATATA, with the plus strand of organelle DNA.
Localization of murine X and autosomal sequences homologous to the human Y located testis-determining region.
Authors: Mitchell M , Simon D , Affara N , Ferguson-Smith M , Avner P , Bishop C
Published: April 2021

Recently a candidate gene for the primary testis-determining factor (TDF) encoding a zinc finger protein (ZFY) has been cloned from the human Y chromosome. A highly homologous X-linked copy has also been identified. Using this human sequence it is possible to identify two Y loci, an X and an autosomal locus in the mouse (Zfy-1, Zfy-2, Zfx and Zfa, respectively). Suprisingly ZFY is more homologous to the mouse X and autosomal sequences than it is to either of the Y-linked loci. Both Zfy-1 and Zfy-2 are present in the Sxr region of the Y but Zfy-2 is absent in the Sxr deletion variant Sxrb (or Sxr") suggesting it is not necessary for male determination. Extensive backcross analyses map Zfa to mouse chromosome 10 and Zfx to a 5-cM interval between anonymous X probe MDXS120 and the tabby locus (Ta). We also show that the mouse androgen receptor locus (m-AR) believed to underlie the testicular feminization mutation (Tfm) shows complete linkage to Zfx. Comparative mapping indicates that in man these genes lie in separate conserved DNA segments.
A set of lacZ mutations in Escherichia coli that allow rapid detection of specific frameshift mutations.
Authors: Cupples C G , Cabrera M , Cruz C , Miller J H
Published: April 2021

We have used site-directed mutagenesis to alter bases in lacZ near the region encoding essential residues in the active site of beta-galactosidase. The altered sequences generate runs of six or seven identical base pairs which create a frameshift, resulting in a Lac- phenotype. Reversion to Lac+ in each strain can occur only by a specific frameshift at these sequences. Monotonous runs of A's (or of T's on the opposite strand) and G's (or C's) have been constructed, as has an alternating -C-G- sequence. These specific frameshift indicator strains complement a set of six previously described strains which detect each of the base substitutions. We have examined a variety of mutagens and mutators for their ability to cause reversion to Lac+. Surprisingly, frameshifts are well stimulated at many of these runs by ethyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine and 2-amino-purine, mutagens not widely known to induce frameshifts. A comparison of ethyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine and 2-aminopurine frameshift specificity with that found with a mutH strain suggests that these mutagens partially or fully saturate or inactivate the methylation-directed mismatch repair system and allow replication errors leading to frameshifts to escape repair. This results in a form of indirect mutagenesis, which can be detected at certain sites.
TRK2 is required for low affinity K+ transport in Saccharomyces cerevisiae.
Authors: Ko C H , Buckley A M , Gaber R F
Published: April 2021

TRK1, the gene encoding the high affinity K+ transporter in Saccharomyces cerevisiae, is nonessential due to the existence of a functionally independent low affinity transporter. To identify the gene(s) encoding the low affinity K+ transporter, we screened trk1 delta cells for mutants (Kla-) that require higher concentrations of K+ in the medium to support growth. trk1 delta trk2 mutants require up to tenfold higher concentrations of K+ to exhibit normal growth compared to trk1 delta TRK2 cells. K+ and 86Rb+ transport assays demonstrate that the mutant phenotype is due to defective K+ transport (uptake). Each of 38 independent mutants contains a mutation in the same gene, TRK2. Cells deficient for both high and low affinity K+ transport (trk1 delta trk2) exhibit hypersensitivity to low extracellular pH that can be suppressed by high concentrations of K+ but not Na+. TRK1 completely suppresses both the K+ transport defect and low pH hypersensitivity of trk2 cells, suggesting that TRK1 and TRK2 are functionally independent.
Direct selection for mutants with increased K+ transport in Saccharomyces cerevisiae.
Authors: Vidal M , Buckley A M , Hilger F , Gaber R F
Published: April 2021

Saccharomyces cerevisiae cells containing a deletion of TRK1, the gene encoding the high affinity potassium transporter, retain only low affinity uptake of this ion and consequently lose the ability to grow in media containing low levels (0.2 mM) of potassium. Using a trk1 delta strain, we selected spontaneous Trk+ pseudorevertants that regained the ability to grow on low concentrations of potassium. The revertants define three unlinked extragenic suppressors of trk1 delta. Dominant RPD2 mutations and recessive rpd1 and rpd3 mutations confer increased potassium uptake in trk1 delta cells. Genetic evidence suggests that RPD2 mutations are alleles of TRK2, the putative low affinity transporter gene, whereas rpd1 and rpd3 mutations increase TRK2 activity: (1) RPD2 mutations are closely linked to trk2, and (2) trk2 mutations are epistatic to both rpd1 and rpd3. rpd1 maps near pho80 on chromosome XV and rpd3 maps on the left arm of chromosome XIV, closely linked to kre1.
stf1: non-wee mutations epistatic to cdc25 in the fission yeast Schizosaccharomyces pombe.
Authors: Hudson J D , Feilotter H , Young P G
Published: April 2021

In Schizosaccharomyces pombe, cdc25 is a cell cycle regulated inducer of mitosis. wee1 and phenotypically wee alleles of cdc2 are epistatic to cdc25. Mutant alleles of a new locus, stf1 (suppressor of twenty-five), identified in a reversion analysis of conditionally lethal cdr1-76 cdc25-22 and cdr2-96 cdc25-22 double mutant strains, also suppress both temperature-sensitive and gene disruption alleles of cdc25. These mutants, by themselves, are phenotypically indistinguishable from wild type strains; hence they represent the first known mutations that are epistatic to cdc25 and do not display a wee phenotype. stf1 genetically interacts with other elements of mitotic control in S. pombe. stf1-1 is additive with wee1-50, cdc2-1w and cdc2-3w for suppression of cdc25-22. Also, like wee1- and cdc2-w, stf1- suppression of cdc25 is reversed by overexpression of the putative type 1 protein phosphatase bws1+/dis2+. Interaction with various mutants and plasmid overexpression experiments suggest that stf1 does not operate either upstream or downstream of wee1. Similarly, it does not operate through cdc25 since it rescues the disruption. stf1 appears to encode an important new element of mitotic control.
Genetic analysis of two female-sterile loci affecting eggshell integrity and embryonic pattern formation in Drosophila melanogaster.
Authors: Degelmann A , Hardy P A , Mahowald A P
Published: April 2021

We have analyzed female-sterile mutations at the X-linked loci fs(1)Nas and fs(1)ph which show allele-specific effects on egg shell structure and embryonic pattern formation. The majority of mutant alleles at both loci lead to a collapsed egg phenotype. The maternal effect lethal phenotype is characterized by cuticle defects resembling those found in three autosomal mutants of the terminal class. We have analyzed the complementation behavior of various heteroallelic combinations at both loci and show that one such combination at the fs(1)Nas locus is capable of restoring normal fertility. We have investigated possible interactions between fs(1)Nas and fs(1)ph and also between the terminal allele of fs(1)Nas and various maternal effect mutations altering the anteroposterior polarity of embryos. We have isolated one new allele of fs(1)Nas which combines the locus-typical phenotypic features with novel cuticle phenotypes. Our results suggest that the products of fs(1)Nas and fs(1)ph are required for the stability of the vitelline membrane and are also involved in a morphogenetic pathway necessary for the correct differentiation of the terminal regions of the embryo. Possible mechanisms to account for the association of these two functions are discussed.
Cis-effects of heterochromatin on heterochromatic and euchromatic gene activity in Drosophila melanogaster.
Authors: Howe M , Dimitri P , Berloco M , Wakimoto B T
Published: April 2021

Chromosomal rearrangements that juxtapose heterochromatin and euchromatin can result in mosaic inactivation of heterochromatic and euchromatic genes. This phenomenon, position effect variegation (PEV), suggests that heterochromatic and euchromatic genes differ in their regulatory requirements. This report describes a novel method for mapping regions required for heterochromatic genes, and those that induce PEV of a euchromatic gene. P transposase mutagenesis was used to generate derivatives of a translocation that variegated for the light+ (lt+) gene and carried the euchromatic white+ (w+) gene on a transposon near the heterochromatin-euchromatin junction. Cytogenetic and genetic analyses of the derivatives showed that P mutagenesis resulted in deletions of several megabases of heterochromatin. Genetic and molecular studies showed that the derivatives shared a euchromatic breakpoint but differed in their heterochromatic breakpoint and their effects on seven heterochromatic genes and the w+ gene. Heterochromatic genes differed in their response to deletions. The lt+ gene was sensitive to the amount of heterochromatin at the breakpoint but the heterochromatic 40Fa gene was not. The severity of variegated w+ phenotype did not depend on the amount of heterochromatin in cis, but varied with local heterochromatic environment. These data are relevant for considering mechanisms of PEV of both heterochromatic and euchromatic genes.
Chromatid and chromosome type breakage-fusion-bridge cycles in wheat (Triticum aestivum L.).
Authors: Lukaszewski A J
Published: April 2021

During the development of disomic additions of rye (Secale cereale L.) chromosomes to wheat (Triticum aestivum L.), two reverse tandem duplications on wheat chromosomes 3D and 4A were isolated. By virtue of their meiotic pairing, the reverse tandem duplications initiated the chromatid type of the breakage-fusion-bridge (BFB) cycle. This BFB cycle continued through pollen mitoses and in the early endosperm divisions, but no clear evidence of its presence in embryo mitoses was found. The chromosome type of BFB cycle was initiated by fusion of two broken chromosome ends resulting in a dicentric or a ring chromosome. Chromosome type BFB cycles were detected in embryo mitoses and in root tips, but they did not persist until the next meiosis and were not transmitted to the progeny. Active BFB cycles induced breakage of other wheat chromosomes that resulted in additional reverse tandem duplications and dicentric and ring chromosomes. Four loci, on chromosome arms 2BS, 3DS, 4AL, and most likely on 7DL, were particularly susceptible to breakage. The BFB cycles produced high frequency of variegation for pigmentation of the aleurone layer of kernels and somatic chimeras for a morphological marker. With the exception of low mutation rate, the observed phenomena are consistent with the activity of a Ds-like element. However, it is not clear whether such an element, if indeed present, was of wheat or rye origin.
Interval mapping of viability loci causing heterosis in Arabidopsis.
Authors: Mitchell-Olds T
Published: April 2021

The genetic basis of heterosis has implications for many problems in genetics and evolution. Heterosis and inbreeding depression affect human genetic diseases, maintenance of genetic variation, evolution of breeding systems, agricultural productivity, and conservation biology. Despite decades of theoretical and empirical studies, the genetic basis of heterosis has remained unclear. I mapped viability loci contributing to heterosis in Arabidopsis. An overdominant factor with large effects on viability mapped to a short interval on chromosome I. Homozygotes had 50% lower viability than heterozygotes in this chromosomal region. Statistical analysis of viability data in this cross indicates that observed viability heterosis is better explained by functional overdominance than by pseudo-overdominance. Overdominance sometimes may be an important cause of hybrid vigor, especially in habitually inbreeding species. Finally, I developed a maximum likelihood interval mapping procedure that can be used to examine chromosomal regions showing segregation distortion or viability selection.
Short-patch reverse transcription in Escherichia coli.
Authors: Thaler D S , Tombline G , Zahn K
Published: April 2021

Chimeras of RNA and DNA have distinctive physical and biological properties. Chimeric oligonucleotides that contained one, two or three ribonucleotides whose phosphodiester backbone was covalently continuous with DNA were synthesized. Site-directed mutagenesis was used to assess genetic information transfer from the ribonucleotide positions. Transfer was scored by the formation or reversion of an ochre site that also corresponded to a restriction cleavage site. This allowed physical as well as genetic assay of mutational events. Bases attached to the ribonucleotides were able to accurately direct the synthesis of progeny DNA. The results suggest that in vivo DNA polymerases utilize a "running start" on a DNA backbone to continue across a covalent backbone junction into a region of ribonucleotides and then back again onto a normal DNA backbone. The phenomenon is designated short-patch reverse transcription (SPRT) by analogy to short-patch mismatch correction and reverse transcription as the term is generally used. The possibility is considered that SPRT contributes to an unrecognized pathway of mutagenesis.
Effects of nullisomic chromosome deficiencies on conjugation events in Tetrahymena thermophila: insufficiency of the parental macronucleus to direct postzygotic development.
Authors: Ward J G , Davis M C , Allis C D , Herrick G
Published: April 2021

Conjugation fails postzygotically after mating of Tetrahymena cells that have wild-type parental macronuclei but harbor noncomplementing nullisomic parental germline deficiencies. Failures begin shortly after formation of the new macronuclear precursor (anlage) and completion of the first step in elimination of the parental macronucleus (pycnosis). Conjugants fail to complete pair separation, to eliminate one new micronucleus, and to amplify anlage DNA, and they eventually die. Some deficiencies block resorption of the pycnotic parental macronucleus, but we find no evidence for its regeneration. Some deficiencies cause aberrant anlage DNA loss. Those that do not cause DNA loss are epistatic to those that do, indicating that normal anlage development requires the dependent function of at least two types of genes. The possibility that these genes are involved in developmentally regulated anlage DNA rearrangements is discussed. Each observed conjugation defect indicates insufficiency of the parental macronucleus to direct postzygotic development and can be explained by the deficiency of essential conjugation genes that are expressed from the anlage. The failure of nullisomic conjugants to complete pair separation indicates a requirement for gene products, expressed from the early anlage or its precursors, soon after anlage first differentiate.
Drosophila-host genetic control of susceptibility to Drosophila C virus.
Authors: Thomas-Orillard M , Jeune B , Cusset G
Published: April 2021

Interactions between Drosophila C virus (DCV) and its natural host, Drosophila melanogaster, were investigated using 15 geographical population samples infected by intraabdominal inoculation. These strains derived from natural populations of D. melanogaster differed in susceptibility to the DCVc. One strain was "partially tolerant". Isofemale lines obtained from one susceptible and one partially tolerant strain were studied. The partially tolerant phenotype was dominant, and there was no difference between F1 progeny of direct and reciprocal crosses. Analysis of F2 progeny showed that neither sex-linked genes nor maternal effects are involved in susceptibility to DCVc. The partially tolerant strain phenotype was dominant and segregated with chromosome III. Two nonexclusive hypotheses are proposed to explain chromosome III gene action.
FRAMESHIFTS AND FRAMESHIFT SUPPRESSORS IN SACCHAROMYCES CEREVISIAE
Authors: Culbertson Michael R , Charnas Lawrence , Johnson M Tina , Fink Gerald R
Published: April 2021

Using ICR-170 as a mutagen, we have induced a set of mutations in yeast which exhibit behavior similar to that shown for bacterial frameshift mutations. Our genetic study shows that these mutations are polar; the polarity can be relieved by internal suppressors; they revert with acridine half-mustards and are not suppressed by known nonsense suppressors. However, they are suppressed by other dominant external suppressors, which fall into two mutually exclusive groups. Five genetically distinct suppressors were obtained for one of these groups, using co-reversion of two frameshift markers. Three of these are lethal in combination with each other and show a reduction in the GLY3 tRNA peak on a Sepharose 4B column. A fourth suppressor shows an altered chromatographic profile for GLY1 tRNA. We suggest that this group of suppressors represent mutations in the structural genes for the isoaccepting glycyl-tRNA's. Two other suppressors (one linked to the centromere of chromosome III) were found to suppress a second group of frameshifts. Genetic and biochemical studies show that the nonMendelian factor [PSI+] increases the efficiency of some frameshift suppressors.
EFFECTS OF ANCESTRAL X IRRADIATION FOLLOWED BY RANDOM MATING ON BODY WEIGHT OF RATS
Authors: Gianola Daniel , Chapman A B , Rutledge J J
Published: April 2021

Effects of nine generations of 450r per generation of ancestral spermatogonial X irradiation of inbred rats on body weight were examined. After six generations of random mating (avoiding inbreeding) following the termination of irradiation, descendants of irradiated males (R) were significantly lighter than their controls (C) at 3 and 6 weeks, but not at 10 weeks of age. However, differences in growth between R and C populations were small. Among-litter and within-litter variance estimates were generally larger in the R lines than in the C lines, suggesting that selection responses would be greater in R than in C lines. In conjunction with previous evidence—obtained during the irradiation phase of the experiment—this suggested that more rapid response to selection for 6-week body weight, in particular, might accrue in the R lines.
EVALUATION OF THE CULLING VARIATE USED BY BREEDERS IN ACTUAL SELECTION
Authors: Yamada Yukio
Published: April 2021

The theoretical basis and computational procedures for estimating the culling variate utilized by breeders in actual selection are presented. The essential part of this procedure is to derive the unknown culling variate in terms of a linear combination of traits based on realized indirect selection differentials of those traits and phenotypic variances and covariances among traits in the population. Special emphasis is placed on the distribution of the variables involved. The accuracy of the culling variate is estimated by use of the biserial correlation with some modifications. Numerical illustrations are given for different types of selection.
ANALYSIS OF THE ROLE OF RECOMBINATION AND REPAIR IN MUTAGENESIS OF ESCHERICHIA COLI BY UV IRRADIATION
Authors: Kato Takesi , Rothman Robert H , Clark Alvin J
Published: April 2021

Multiple mutant strains have been tested for their mimicry of the UV-mutagenesis deficiency of a recA single mutant. Revertants to histidine prototrophy and clear plaque mutants of lambda were scored to determine capacity for UV-mutagenesis. Nearly normal capacity was shown by a uvr  +  recB  -  recF  - strain, which shows almost no recA-dependent recombination, by uvr  -  recB  +  recF  - strains, which show almost no recA-dependent repair and by a uvrA  -  recB  -  recF  - strain, which shows neither recA-dependent recombination nor repair. Since the uvr mutants can be assumed to show additionally no excision repair, these results may mean that UV-mutagenesis occurs during processes other than recombination and repair. Alternative hypotheses are discussed. The slight difference in mutagenic capacity was traced to the recF single mutation, which blocks the production of unmixed bursts of clear-plaque lambda mutants. Since this accounts for only about 10% of the mutations leading to clear-plaque mutants, it is suggested that there is more than one UV-mutagenic process.
STUDIES IN THE DYNAMICS OF GENETICALLY VARIABLE POPULATIONS. I. FREQUENCY- AND DENSITY-DEPENDENT SELECTION IN EXPERIMENTAL POPULATIONS OF DROSOPHILA MELANOGASTER
Authors: DeBenedictis Paul A
Published: April 2021

Changes in genetic composition and in fitness of karyotypes in synthetic populations of Drosophila melanogaster carrying fourth chromosomes marked with recessive mutants in repulsion were measured as functions of initial population composition and density. There was no detectable influence of initial population density on the magnitude of chromosome frequency change or on adaptive values of karyotypes, but both measures proved sensitive to population composition. That fitness be measured zygote-to-zygote is argued to be of dubious necessity in all contexts except demonstration of frequency-dependent selection. Some prior reports cited as evidence of the operation of density-dependent selection, like the present study, contain no evidence that the rate of natural selection is influenced by population crowding. Reports that do demonstrate density-dependent selection suggest that the relationship between fitness and crowding differs from that assumed in most theoretical treatments. Further work is needed to elucidate the interaction between fitness, population crowding, and population composition.
MUTATIONS INCREASING ASEXUAL PLASMODIUM FORMATION IN PHYSARUM POLYCEPHALUM
Authors: Adler Paul N , Holt Charles E
Published: April 2021

Rare plasmodia formed in clones of heterothallic amoebae were analyzed in a search for mutations affecting plasmodium formation. The results show that the proportion of mutants varies with both temperature (18°, 26° or 30°) and mating-type allele (mt1, mt2, mt3, mt4). At one extreme, only one of 33 plasmoida formed by mt2 amoebae at 18° is mutant. At the other extreme, three of three plasmodia formed by mt1 amoebae at 30° are mutant. The mutant plasmodia fall into two groups, the GAD (greater asexual differentiation) mutants and the ALC (amoebaless life cycle) mutants. The spores of GAD mutants give rise to amoebae that differentiate into plasmodia asexually at much higher frequencies than normal heterothallic amoebae. Seven of eight gad mutations analyzed genetically are linked to mt and one (gad-12) is not. The gad-12 mutation is expressed in strains with different alleles of mt. The frequency of asexual plasmodium formation is heat sensitive in some (e.g., mt3 gad-11), heat-insensitive in two (mt2 gad-8 and mt2 gad-9) and cold-sensitive in one (mt1 gad-12) of twelve GAD mutants analyzed phenotypically. The spores of ALC mutants give rise to plasmodia directly, thereby circumventing the amoebal phase of the life cycle. Spores from five of the seven ALC mutants give rise to occasional amoebae, as well as plasmodia. The amoebae from one of the mutants carry a mutation (alc-1) that is unlinked to mt and is responsible for the ALC phenotype in this mutant. Like gad-12, alc-1 is expressed with different mt alleles. Preliminary observations with amoebae from the other four ALC mutants suggest that two are similar to the one containing alc-1; one gives rise to revertant amoebae, and one gives rise to amoebae carrying an alc mutation and a suppressor of the mutation.
LINKAGE AND GENETIC MAP LENGTH IN TETRAHYMENA THERMOPHILA
Authors: McCoy J Wynne
Published: April 2021

The genetic map of T. thermophila has been extended with tests of over 170 marker combinations. Three linkage groups have been identified, in addition to several apparent linkages which are seen only when certain strains are used. A sampling argument was developed to estimate the total genetic map length from the observed fraction of marker combinations showing linkage. If the strain-dependent linkages are actually due to structural heterozygosity, the total map length is estimated at about 1,200 cM.
DOMINANT CHROMOSOMAL MUTATION BYPASSING CHROMOSOMAL GENES NEEDED FOR KILLER RNA PLASMID REPLICATION IN YEAST
Authors: Wickner Reed B , Leibowitz Michael J
Published: April 2021

Yeast strains carrying a double-stranded RNA plasmid of 1.4-1.7 × 106 daltons encapsulated in virus-like particles secrete a toxin that kills strains lacking this plasmid. The plasmid requires at least 24 chromosomal genes (pets, and mak1 through mak23) for its replication or maintenance. We have detected dominant Mendelian mutations (called KRB1 for killer replication bypass) that bypass two chromosomal genes, mak7 and pets, normally needed for plasmid replication. Strains mutant in mak7 and carrying the bypass mutation (mak7-1 KRB1) are isolated as frequent K+R+ sectors of predominantly K-R- segregants from crosses of mak7-1 with a wild-type killer. All KRB1 mutations isolated in this way are inherited as single dominant centromere-linked chromosomal changes. They define a new centromere. KRB1 is not a translational suppressor. KRB1 strains contain a genetically normal killer plasmid and ds RNA species approximately the same in size and amount as do wild-type killers. Bypass of both mak7 and pets by one mutation suggests that these two genes are functionally related.

Two properties of the inheritance of KRB1 indicate an unusually high reversion frequency: (1) Heat or cycloheximide (treatments known to cure strains of the wild-type killer plasmid) readily induce conversion of mak7-1 KRB1 strains from killers to nonkillers with concomitant disappearance of KRB1 as judged by further crosses, and (2) mating two strains of the type mak7-1 KRB1 with each other yields mostly 2 K+R+: 2 K-R- segregation, although the same KRB1 mutation and the same killer plasmid are present in both parents.
X-RAY-INDUCED CHROMOSOME ABERRATIONS IN MOUSE DICTYATE OOCYTES. II. FRACTIONATION AND DOSE RATE EFFECTS
Authors: Brewen J G , Payne H S , Adler I D
Published: April 2021

Split-dose experiments were done on maturing dictyate oocytes to determine if the magnitude of the first dose influenced the "rejoining time" of radiation-induced chromosomal lesions. A total dose of 400r was split into various combinations with varying fractionation intervals. The data derived from analyzing interchanges indicate that there is no difference in the rejoining time whether the first dose was 100, 200, or 300r. It thus appears that the radiation dose in the ranges studied does not significantly alter the rate of repair of the chromosomal lesions. This conclusion is contrary to that which has been propounded to explain the nonlinear dose curves obtained for specific locus mutations.

Chronic 60Co Υ-ray exposures were given to female mice over an 8-day period. The exposures were delivered during the period of peak sensitivity, i.e., 8-16 days prior to ovulation. The doses given were 117, 240, 348, and 483r. The aberration yields observed were dramatically lower than for comparable doses of acute X rays even when the RBE of Υ rays compared with X rays is taken into account. The large drop in yields at the low dose rates is interpreted as resulting from a large two-track component in the acute curve, and as being independent of effects on repair systems.
EXAMINATION OF ALLELIC VARIATION AT THE HEXOKINASE LOCI OF DROSOPHILA PSEUDOOBSCURA AND D. PERSIMILIS BY DIFFERENT METHODS
Authors: Beckenbach Andrew T , Prakash Satya
Published: April 2021

Recently a number of electrophoretic techniques have been applied to reveal the presence of additional genetic variation among the electrophoretic mobility classes of the highly polymorphic xanthine dehydrogenase (XDH) and esterase-5 (est-5) loci. We examined the hexokinase loci of Drosophila pseudoobscura and D. persimilis using a variety of techniques to determine whether further allelic variation could be revealed for these much less polymorphic loci and to analyze the nature of the known variation at the hexokinase-1 (hex-1) locus. The following studies were conducted: 135 strains of the two species from six localities were examined with buffer pH ranging from 5.5 to 10.0; 40 strains of D. pseudoobscura and 9 strains of D. persimilis from Mather were studied using starch gel concentrations ranging from 8.5 to 15.5% and were examined for differences in heat stability and reactivity to the thiol reagent p CMSA; strains were also tested for susceptibility to urea denaturation and differences in relative activities. Major findings of the work are: (1) No additional allelic variation could be detected at any of the hexokinase loci by applying these techniques. The finding of abundant hidden genetic variation in XDH and est-5 does not extend to all enzyme loci. (2) Evidence from studies using p CMSA indicates that the hex-1 alleles 0.6, 0.8, 1.0 and 1.2 of the two species form a series of unit charge steps. Since the 0.94 allele of D. persimilis has mobility intermediate between 0.8 and 1.0, it is argued that routine electrophoretic techniques are sensitive to at least some conservative amino acid substitutions. (3) Strong correlations were found at the hex-1locus between low allelic frequency, reduced relative activity and reduced stability to heat and urea denaturation. Since the three sibling species, D. pseudoobscura, D. persimilis and D. miranda, all appear to share a common high frequency allele (1.0) at that locus, these findings are taken as evidence that the observed allelic frequencies are a result of directional selection and mutation, rather than any form of balancing selection.
GENETIC ANALYSIS OF A POPULATION OF TRIBOLIUM. VI. POLYMORPHISM AND DEMOGRAPHIC EQUILIBRIUM
Authors: Moffa A M , Costantino R F
Published: April 2021

Demographic and genetic data of continuously growing populations of Tribolium castaneum initiated with identical age structures but with different frequencies of the unsaturated fatty acid-sensitive allele were collected for 68 weeks.—The life history data provided the following insights: Genotypic differences for total number of offspring were due primarily to larval viability. The total lifetime offspring production of the genotypes predicted a stable polymorphic genetic equilibrium. The genotypic reproductive functions forecast that a stable age structure was not a prerequisite for genetic equilibrium.—Those cultures initially segregating for the unsaturated fatty acid-sensitive allele converged to an equilibrium allele frequency of 0.25 and a genotypic array composed of equal numbers of +/+ and +/cos individuals.—The numbers of larvae, pupae and adults during the first six weeks were quadratic functions of the initial frequency of the sensitive allele. Qualitative age structure changes that followed were similar in all cultures and demographic equilibrium was realized at week 50. The overall demographic pattern during the 68-week study was interpreted in terms of the interactions among the numbers of small larvae, large larvae plus pupae, and adults.
PROPERTIES OF EQUILIBRIA IN MULTI-LOCUS GENETIC SYSTEMS
Authors: Ewens Warren J , Thomson Glenys
Published: April 2021

The classical mathematical theory of population genetics considered, for simplicity, almost exclusively one-locus systems. In the last two decades much work has been done on two-locus and, less frequently, multi-locus systems. This research has usually involved investigating properties of systems with given, and usually rather special, fitness parameters. Real genetic fitness systems are undoubtedly multi-locus and seldom will possess simplifying characteristics. One aim of this paper is to study generalized systems where no special assumptions are made about fitness structure, the number of alleles at each locus, the number of loci involved or the recombination structure between loci. A second aim is to consider marginal properties (often one-locus properties) of complex systems: the fact that many observations involve data from only one locus makes this second aim relevant.
HERITABILITY OF QUASI-CONTINUOUS SKELETAL TRAITS IN A RANDOMBRED POPULATION OF HOUSE MICE
Authors: Self Steven G , Leamy Larry
Published: April 2021

Heritabilities of 11 quasi-continuous skeletal traits were estimated in randombred house mice of three separate ages (1, 3, and 5 months). Three separate methods-regression, maximum likelihood correlation, and Falconer's Method-were used to obtain heritabilities for each of the separate age groups. Significant differences in the incidences of seven of the skeletal traits were found among ages, but they did not affect the heritability estimates, these estimates being pooled over ages. Heritabilities calculated from female parents were consistently higher (by about 13%) than those from male parents, indicating the presence of maternal effects. Mid-parent estimates made by all three methods gave very similar mean levels (0.17 - 0.20). Although low, this level compared favorably with that expected on the basis of previously estimated rates of accumulation of genetic variance. Maternal effects estimated from full sib correlations averaged 0.08.