bluuebunny/crossref_metadata_2025_split huggingface dataset:
An intragenic suppressor of a calmodulin mutation in Paramecium: genetic and biochemical characterization.
Authors: Hinrichsen R D , Pollock M , Hennessey T , Russell C 
Published: January 2021

Abstract
We describe a suppressor of the calmodulin mutant cam1 in Paramecium tetraurelia. The cam1 mutant, which has a SER----PHE change at residue 101 of the third calcium-binding domain, inhibits the activity of the Ca(2+)-dependent K+ current and causes exaggerated behavioral responses to most stimuli. An enrichment scheme, based on an increased sensitivity to Ba2+ in cam1 cells, was used to isolate suppressors. One such suppressor, designated cam101, restores both the activity of the Ca(2+)-dependent K+ current and behavioral responses of the cells. We show that the cam101 mutant is an intragenic suppressor of cam1, based on genetic and microinjection data. The cam101 calmodulin is shown to be similar to wild-type calmodulin in terms of its ability to stimulate calmodulin-dependent phosphodiesterase at low concentrations of free calcium. However, the cam101 calmodulin has a reduced affinity for a monoclonal antibody to wild-type Paramecium calmodulin, as does the parental cam1 calmodulin, and a different mobility on acid-urea gels relative to both wild-type and cam1 calmodulin. We have been able to demonstrate that the isolation of intragenic suppressors of a calmodulin mutation is possible, which allows for the further genetic analysis of structure-function relationships in the calmodulin molecule.
Cloning of the Mutator transposable element MuA2, a putative regulator of somatic mutability of the a1-Mum2 allele in maize.
Authors: Qin M M , Robertson D S , Ellingboe A H 
Published: January 2021

Abstract
The identification of the autonomous or transposase-encoding element of the Mutator (Mu) transposable element system of maize is necessary to the characterization of the system. We reported previously that a transcript homologous to the internal region of the MuA element is associated with activity of the Mutator system. We describe here the cloning of another Mu element, designated MuA2, that cosegregates with Mutator activity as assayed by somatic instability of the a1-Mum2 allele. The MuA2 element has features typical of the transposable elements of the Mutator family, including the 210-bp terminal inverted repeats. Several lines of evidence suggest that MuA2 is an autonomous or transposase-encoding element of the Mu family: (1) MuA2 cosegregates with a genetically defined element that regulates somatic mutability of the a1-Mum2 allele; (2) MuA2 is hypomethylated while most other MuA2-hybridizing sequences in the genome are extensively methylated; (3) the increase of the copy number of MuA2 is concomitant with the increase of regulator elements; (4) MuA2-like elements are found in Mutator lines but not in non-Mutator inbreds. We propose that autonomous or transposase-encoding elements of the Mu family may be structurally conserved and MuA2-like.
Age-dependent sexually asymmetric selection: the use of intrinsic values.
Authors: Gregorius H R 
Published: January 2021

Abstract
To study the evolutionary role played by differential male and female fertility (sexual asymmetry) both between individuals and over the life span within single individuals, the terms "intrinsic male fertility" and "intrinsic female fertility" are introduced. With the help of these terms, the concept of sexual asymmetry can be made precise and its effect on the establishment and maintenance of genetic polymorphisms can be analyzed. The main conclusions are: (1) any mutant causing a modification of the male fertility parameters which result in an increased intrinsic male fertility becomes established; (2) a corollary of this is that age-specific sexual asymmetry, as results from alternating degrees of female and male flowering in successive reproduction cycles, for example, has only secondary effects on the initial growth rate; (3) under the biologically reasonable premise that modifications of life histories result from reallocation of fixed net reproduction resources (defined as constant total female and male net reproduction output), a shift of net reproduction (whether female, male, or both in arbitrary proportions) to earlier ages is evolutionarily successful in growing but not in declining populations; shifts of net reproduction to later ages have opposite consequences.
Ability of a bacterial chromosome segment to invert is dictated by included material rather than flanking sequence.
Authors: Mahan M J , Roth J R 
Published: January 2021

Abstract
Homologous recombination between sequences present in inverse order within the same chromosome can result in inversion formation. We have previously shown that inverse order sequences at some sites (permissive) recombine to generate the expected inversion; no inversions are found when the same inverse order sequences flank other (nonpermissive) regions of the chromosome. In hopes of defining how permissive and nonpermissive intervals are determined, we have constructed a strain that carries a large chromosomal inversion. Using this inversion mutant as the parent strain, we have determined the "permissivity" of a series of chromosomal sites for secondary inversions. For the set of intervals tested, permissivity seems to be dictated by the nature of the genetic material present within the chromosomal interval being tested rather than the flanking sequences or orientation of this material in the chromosome. Almost all permissive intervals include the origin or terminus of replication. We suggest that the rules for recovery of inversions reflect mechanistic restrictions on the occurrence of inversions rather than lethal consequences of the completed rearrangement.
An unusual genomic position effect on Drosophila white gene expression: pairing dependence, interactions with zeste, and molecular analysis of revertants.
Authors: Hazelrigg T , Petersen S 
Published: January 2021

Abstract
The white gene in the AR4-24 P[white,rosy] insertion on chromosome 2 has a novel expression pattern, in which it is repressed in the dorsal half of the eye. X-ray mutagenesis led to the isolation of six revertants mapping to chromosome 2, which are wild type in a zeste+ background, and three extreme derivatives, in which white gene expression is repressed in ventral regions of the eye as well. By Southern blot analyses the breakpoints of five of the revertants and one of the extreme derivatives were mapped in the flanking DNA bordering each side of the AR4-24 insertion. The revertants show some dorsal repression of white in the presence of z1, and by this criterion each is only a partial revertant. The extreme derivatives act not only in cis, but also in trans to repress expression of AR4-24 and its various derivatives. We provide evidence that these trans effects are proximity-dependent effects, possibly mediated by pairing of gene copies, as they do not extend to copies of the white gene located elsewhere in the genome. We show that one extreme derivative, E1, is a small deletion spanning the insertion site at the 5' end of the white gene, and propose that the distance between a negative regulatory element in the 5' flanking DNA and the white promoter influences the degree of the repression.
A restriction fragment length polymorphism map and electrophoretic karyotype of the fungal maize pathogen Cochliobolus heterostrophus.
Authors: Tzeng T H , Lyngholm L K , Ford C F , Bronson C R 
Published: January 2021

Abstract
A restriction fragment length polymorphism (RFLP) map has been constructed of the nuclear genome of the plant pathogenic ascomycete Cochliobolus heterostrophus. The segregation of 128 RFLP and 4 phenotypic markers was analyzed among 91 random progeny of a single cross; linkages were detected among 126 of the markers. The intact chromosomal DNAs of the parents and certain progeny were separated using pulsed field gel electrophoresis and hybridized with probes used to detect the RFLPs. In this way, 125 markers were assigned to specific chromosomes and linkages among 120 of the markers were confirmed. These linkages totalled 941 centimorgans (cM). Several RFLPs and a reciprocal translocation were identified tightly linked to Tox1, a locus controlling host-specific virulence. Other differences in chromosome arrangement between the parents were also detected. Fourteen gaps of at least 40 cM were identified between linkage groups on the same chromosomes; the total map length was therefore estimated to be, at a minimum, 1501 cM. Fifteen A chromosomes ranging from about 1.3 megabases (Mb) to about 3.7 Mb were identified; one of the strains also has an apparent B chromosome. This chromosome appears to be completely dispensable; in some progeny, all of 15 markers that mapped to this chromosome were absent. The total genome size was estimated to be roughly 35 Mb. Based on these estimates of map length and physical genome size, the average kb/cM ratio in this cross was calculated to be approximately 23. This low ratio of physical length to map distance should make this RFLP map a useful tool for cloning genes.
Genetic changes accompanying increased fitness in evolving populations of Escherichia coli.
Authors: Modi R I , Castilla L H , Puskas-Rozsa S , Helling R B , Adams J 
Published: January 2021

Abstract
Two populations of Escherichia coli, each initiated with a single clone containing a derivative of the plasmid pBR322, were maintained for long periods in glucose-limited continuous culture. In both populations, after an extensive number of generations had elapsed, clones were isolated in which the transposon Tn3 from the plasmid had integrated into the bacterial chromosome. In both cases examined, the transpositions were shown to increase relative fitness approximately 6-7%, in the environment in which the populations were maintained. The loci of integration were mapped to approximately 13.2 min (population 1) and approximately 32.8 min (population 2).
Elimination of the yeast RAD6 ubiquitin conjugase enhances base-pair transitions and G.C----T.A transversions as well as transposition of the Ty element: implications for the control of spontaneous mutation.
Authors: Kang X L , Yadao F , Gietz R D , Kunz B A 
Published: January 2021

Abstract
The RAD6 gene of the yeast Saccharomyces cerevisiae encodes an enzyme that conjugates ubiquitin to other proteins. Defects in RAD6 confer a mutator phenotype due, in part, to an increased rate of transposition of the yeast Ty element. To further delineate the role of protein ubiquitination in the control of spontaneous mutagenesis in yeast, we have characterized 202 mutations that arose spontaneously in the SUP4-o gene carried on a centromere vector in a RAD6 deletion strain. The resulting mutational spectrum was compared to that for 354 spontaneous SUP4-o mutations isolated in the isogenic wild-type parent. This comparison revealed that the rad6 mutator enhanced the rate of single base-pair substitution, as well as Ty insertion, but did not affect the rates of the other mutational classes detected. Relative to the wild-type parent, Ty inserted at considerably more SUP4-o positions in the rad6 strain with a significantly smaller fraction detected at a transposition hotspot. These findings suggest that, in addition to the rate of transposition, protein ubiquitination might influence the target site specificity of Ty insertion. The increase in the substitution rate accounted for approximately 90% of the rad6 mutator effect but only the two transitions and the G. C----T.A transversion were enhanced. Analysis of the distribution of these events within SUP4-o suggested that the site specificity of the substitutions was influenced by DNA sequence context. Transformation of heteroduplex plasmid DNAs into the two strains demonstrated that the rad6 mutator did not reduce the efficiency of correcting mismatches that could give rise to the transitions or transversion nor did it bias restoration of the mismatches to the incorrect base-pairs. These results are discussed in relation to possible mechanisms that might link ubiquitination of proteins to spontaneous mutation rates.
Simultaneous gain and loss of functions caused by a single amino acid substitution in the beta subunit of Escherichia coli RNA polymerase: suppression of nusA and rho mutations and conditional lethality.
Authors: Sparkowski J , Das A 
Published: January 2021

Abstract
Transcript elongation and termination in Escherichia coli is modulated, in part, by the nusA gene product, an acidic protein that interacts not only with RNA polymerase itself but also with ancillary factors, namely the host termination protein Rho and phage lambda antitermination protein, N. The E. coli nusA1 mutant fails to support lambda development due to a specific defect in N-mediated antitermination. Certain rifampicin-resistant (rifR) variants of the nusA1 host support lambda growth. We report here the isolation and pleiotropic properties of one such rifR mutant, ts8, resulting from a single amino acid substitution mutation in rpoB, the structural gene for polymerase beta subunit. ts8 is a recessive lethal mutation that blocks cell growth at 42 degrees. Pulse-labeling and analysis of newly synthesized proteins indicate that the mutant cell is proficient in RNA synthesis at high temperature. Apparently, ts8 causes a loss of some specialized function of RNA polymerase without a gross defect in general transcription activities. ts8 is an allele-specific suppressor of nusA1. It does not suppress nusAsal, nusB5 and nusE71 mutations nor does it bypass the requirement for a functional N gene and the nut site for antitermination and lambda growth. A mutation in the N gene, punA1, that restores lambda growth in the nusA1 mutant host but not in the nusAsal host, compensates for the nusAsal allele in the ts8 mutant. This combined effect of two allele-specific suppressors suggests that they enhance some aspect of polymerase-NusA-N interaction and function. ts8 suppresses the rho15 mutation, but not the rho112 mutation, indicating that it might render RNA polymerase susceptible to the action of a defective Rho protein. Marker rescue analysis has localized ts8 to a 910-bp internal segment of rpoB that encodes the Rif domain. By amplification, cloning and sequencing of this segment of the mutant chromosome we have determined that ts8 contains Phe in place of Ser522, caused by a C to T transition. By gene conversion, we have established that the simultaneous gain and loss of three functions of polymerase is caused by this single amino acid substitution. Clearly, a site in the beta subunit critical for the functioning of both termination and antitermination factors is altered by ts8. The alteration, we imagine, might make this site on polymerase receptive to some factors but repulsive to others.
An empirical test of the meiotic drive models of hybrid sterility: sex-ratio data from hybrids between Drosophila simulans and Drosophila sechellia.
Authors: Johnson N A , Wu C I 
Published: January 2021

Abstract
Recently, there has been much discussion regarding the hypothesis that divergence of meiotic drive systems in isolated populations can generate the patterns of reproductive isolation observed in animal hybridizations. One prediction from this hypothesis is that the sex ratio of hybrids with heterospecific sex chromosomes should greatly deviate from the Mendelian expectation of 50% female. From sex-ratio data in our Drosophila hybridization studies, we find no such deviation: the sex ratio of offspring of males with introgressed heterospecific Y chromosomes with various autosomal backgrounds does not differ from that of the pure species. We also discuss other aspects of the current meiotic drive models.
Estimates of gene flow among populations, geographic races, and species in the Ipomopsis aggregata complex.
Authors: Wolf P G , Soltis P S 
Published: January 2021

Abstract
Interpopulational gene flow within a species can reduce population differentiation due to genetic drift, whereas genetic exchange among taxa can impede speciation. We used allozyme data to estimate gene flow within and among geographic races and species of perennial herbs in the Ipomopsis aggregata complex (Polemoniaceae). Estimates of interpopulational gene flow within taxa from two methods (F statistics and private alleles) were correlated with one another. Gene flow among populations within each geographic race (subspecies) of I. aggregata was relatively high (Nm greater than approximately 1.0). Gene flow was also high among populations of I. arizonica and among four northern populations of I. tenuituba. However, gene flow was low (Nm less than 1.0) for I. tenuituba when a population representing subsp. macrosiphon was included. This is consistent with previous findings that subsp. macrosiphon has had an independent origin and is reproductively, as well as geographically, isolated. A recently developed model, based on hierarchical F statistics, was employed to estimate genetic exchange among taxa. Gene flow estimates were generally high among races of I. aggregata (dNmrace greater than 1.0) but were low among subspecies of I. tenuituba (dNmrace less than 1.0). Consistent with morphological evidence, estimates of interspecific gene flow were moderate between I. aggregata and I. tenuituba, which hybridize in several areas. However, contrary to morphological evidence, we estimated relatively high levels of interspecific gene flow involving I. arizonica. Our results suggest that I. arizonica has hybridized with other species without the transfer of morphological traits.(ABSTRACT TRUNCATED AT 250 WORDS)
par-4, a gene required for cytoplasmic localization and determination of specific cell types in Caenorhabditis elegans embryogenesis.
Authors: Morton D G , Roos J M , Kemphues K J 
Published: January 2021

Abstract
Specification of some cell fates in the early Caenorhabditis elegans embryo is mediated by cytoplasmic localization under control of the maternal genome. Using nine newly isolated mutations, and two existing mutations, we have analyzed the role of the maternally expressed gene par-4 in cytoplasmic localization. We recovered seven new par-4 alleles in screens for maternal effect lethal mutations that result in failure to differentiate intestinal cells. Two additional par-4 mutations were identified in noncomplementation screens using strains with a high frequency of transposon mobility. All 11 mutations cause defects early in development of embryos produced by homozygous mutant mothers. Analysis with a deficiency in the region indicates that it33 is a strong loss-of-function mutation. par-4(it33) terminal stage embryos contain many cells, but show no morphogenesis, and are lacking intestinal cells. Temperature shifts with the it57ts allele suggest that the critical period for both intestinal differentiation and embryo viability begins during oogenesis, about 1.5 hr before fertilization, and ends before the four-cell stage. We propose that the primary function of the par-4 gene is to act as part of a maternally encoded system for cytoplasmic localization in the first cell cycle, with par-4 playing a particularly important role in the determination of intestine. Analysis of a par-4; par-2 double mutant suggests that par-4 and par-2 gene products interact in this system.
A comprehensive study of genic variation in natural populations of Drosophila melanogaster. VI. Patterns and processes of genic divergence between D. melanogaster and its sibling species, Drosophila simulans.
Authors: Choudhary M , Coulthart M B , Singh R S 
Published: January 2021

Abstract
We present here an extensive set of data on allelic differences between homologous proteins of Drosophila melanogaster and its sibling species, Drosophila simulans, obtained by nondenaturing one-dimensional, and denaturing two-dimensional gel electrophoresis. The data suggest that, for these two species, (1) approximately 10% of protein-coding loci have no alleles in common in our sample, (2) the extent of genic variation at a locus (mean heterozygosity) within a species is not correlated with the extent of divergence (Nei's genetic distance) at that locus between species, and (3) significant heterogeneity of divergence rates exists for different structural/functional classes of loci. These results are discussed in the context of the dynamics of genetic variation within and between species.
Global population genetic structure and male-mediated gene flow in the green turtle (Chelonia mydas): RFLP analyses of anonymous nuclear loci.
Authors: Karl S A , Bowen B W , Avise J C 
Published: January 2021

Abstract
We introduce an approach for the analysis of Mendelian polymorphisms in nuclear DNA (nDNA), using restriction fragment patterns from anonymous single-copy regions amplified by the polymerase chain reaction, and apply this method to the elucidation of population structure and gene flow in the endangered green turtle, Chelonia mydas. Seven anonymous clones isolated from a total cell DNA library were sequenced to generate primers for the amplification of nDNA fragments. Nine individuals were screened for restriction site polymorphisms at these seven loci, using 40 endonucleases. Two loci were monomorphic, while the remainder exhibited a total of nine polymorphic restriction sites and three size variants (reflecting 600-base pair (bp) and 20-bp deletions and a 20-bp insertion). A total of 256 turtle specimens from 15 nesting populations worldwide were then scored for these polymorphisms. Genotypic proportions within populations were in accord with Hardy-Weinberg expectations. Strong linkage disequilibrium observed among polymorphic sites within loci enabled multisite haplotype assignments. Estimates of the standardized variance in haplotype frequency among global collections (FST = 0.17), within the Atlantic-Mediterranean (FST = 0.13), and within the Indian-Pacific (FST = 0.13), revealed a moderate degree of population substructure. Although a previous study concluded that nesting populations appear to be highly structured with respect to female (mitochondrial DNA) lineages, estimates of Nm based on nDNA data from this study indicate moderate rates of male-mediated gene flow. A positive relationship between genetic similarity and geographic proximity suggests historical connections and/or contemporary gene flow between particular rookery populations, likely via matings on overlapping feeding grounds, migration corridors or nonnatal rookeries.
Associations between nuclear loci and chloroplast DNA genotypes in wild barley.
Authors: Maroof M A , Zhang Q , Neale D B , Allard R W 
Published: January 2021

Abstract
Associations among alleles at nine nuclear loci and three chloroplast DNA (cpDNA) genotypes were assessed in a sample of 247 accessions of the wild barley, Hordeum vulgare ssp. spontaneum. Alleles at two of the nine nuclear loci are marked by length variations in the intergenic spacer region of ribosomal DNA (rDNA), and those of the other seven loci are well characterized allozymes. The three chloroplast DNA (cpDNA) genotypes are marked by restriction fragment length polymorphisms resulting from three polymorphic restriction sites detected by Southern blot hybridization. The analyses were performed by dividing the nine nuclear loci into a series of two-locus subsets and constructing log-linear models to characterize associations between the subsets of two nuclear loci and the cpDNA genotypes. Statistically significant associations were detected between six of the nine nuclear loci and the cpDNA genotypes, either individually as pairwise correlations, or through interaction with another nuclear locus to form three-variate complexes. Although the sample size of the present study was inadequate for statistical evaluation of higher order interactions, the results suggest the existence of interactions in which more than two nuclear loci are involved in associations with cpDNA genotypes. The observed cytonuclear associations appear to result from interplay among a number of evolutionary forces including a mating system of predominant selfing, differentiation among gene pools of local populations, and adaptation of barley genotypes to specific environmental conditions.