bluuebunny/crossref_metadata_2025 huggingface dataset:
BACTERIOPHAGE T4 ENDONUCLEASES II AND IV, OPPOSITELY AFFECTED BY dCMP HYDROXYMETHYLASE ACTIVITY, HAVE DIFFERENT ROLES IN THE DEGRADATION AND IN THE RNA POLYMERASE-DEPENDENT REPLICATION OF T4 CYTOSINE-CONTAINING DNA
Authors: Carlson Karin , Ȗvervatin Aud
Published: January 2021

Bacteriophage T4 mutants defective in gene 56 (dCTPase) synthesize DNA where cytosine (Cyt) partially or completely replaces hydroxymethylcytosine (HmCyt). This Cyt-DNA is degraded in vivo by T4 endonucleases II and IV, and by the exonuclease coded or controlled by genes 46 and 47.—Our results demonstrate that T4 endonuclease II is the principal enzyme initiating degradation of T4 Cyt-DNA. The activity of endonuclease IV, but not that of endonuclease II, was stimulated in the presence of a wild-type dCMP hydroxymethylase, also when no HmCyt was incorporated into phage DNA, suggesting the possibility of direct endonuclease IV-dCMP hydroxymethylase interactions. Endonuclease II activity, on the other hand, was almost completely inhibited in the presence of very small amounts of HmCyt (3-9% of total Cyt + HmCyt) in the DNA. Possible mechanisms for this inhibition are discussed.—The E. coli RNA polymerase modified by the products of T4 genes 33 and 55 was capable of initiating DNA synthesis on a Cyt-DNA template, although it probably cannot do so on an HmCyt template. In the presence of an active endonuclease IV, Cyt-DNA synthesis was arrested 10-30 min after infection, probably due to damage to the template. Cyt-DNA synthesis dependent on the unmodified (33  -  55  -) RNA polymerase was less sensitive to endonuclease IV action.
GENERAL NONCHEMOTACTIC MUTANTS OF CAULOBACTER CRESCENTUS
Authors: Ely Bert , Gerardot Connie J , Fleming Donna L , Gomes Suely L , Frederikse Peter , Shapiro Lucille
Published: January 2021

We have examined 35 mutants that have defects in general chemotaxis. Genetic analysis of these mutants resulted in the identification of at least eight che genes located at six different positions on the Caulobacter crescentus chromosome. The cheR, cheB and cheT genes appeared to be located in a three-gene cluster. Mutations in these three genes resulted in the inability of the flagellum to reverse the direction of rotation. Defects in the cheR gene resulted in a loss of the ability to methylate the methyl-accepting chemotaxis proteins. In vitro experiments showed that the lack of in vivo methylation in cheR mutants was due to the absence of methyltransferase activity. Defects in the cheB gene resulted in greatly reduced chemotaxis-associated methylation in vivo and a loss of methylesterase activity in vitro. The specific defects responsible for the lack of a chemotactic response have not been determined for the other identified che genes.
THE SELECTION LIMIT DUE TO THE CONFLICT BETWEEN TRUNCATION AND STABILIZING SELECTION WITH MUTATION
Authors: Zeng Zhao-Bang , Hill William G
Published: January 2021

Long-term selection response could slow down from a decline in genetic variance or in selection differential or both. A model of conflict between truncation and stabilizing selection in infinite population size is analysed in terms of the reduction in selection differential. Under the assumption of a normal phenotypic distribution, the limit to selection is found to be a function of κ, the intensity of truncation selection, ω 2, a measure of the intensity of stabilizing selection, and σ 2, the phenotypic variance of the character. The maintenance of genetic variation at this limit is also analyzed in terms of mutation-selection balance by the use of the "House-of-cards" approximation. It is found that truncation selection can substantially reduce the equilibrium genetic variance below that when only stabilizing selection is acting, and the proportional reduction in variance is greatest when the selection is very weak. When truncation selection is strong, any further increase in the strength of selection has little further influence on the variance. It appears that this mutation-selection balance is insufficient to account for the high levels of genetic variation observed in many long-term selection experiments.
Synthesis of a trans-Acting Inhibitor of DNA Maturation by Prohead Mutants of Phage Λ
Authors: Murialdo Helios , Fife Wendy L
Published: January 2021

Bacteriophage λ with mutations in genes that control prohead assembly and other head precursors cannot mature their DNA. In this paper we present evidence that the failure of these phage mutants to mature DNA is a reflection of a mechanism that modulates terminase nicking activity during normal phage development. We have constructed plasmids that contain the λ-cohesive end site (cos) and the genes that code for DNA terminase, the enzyme that matures DNA by cutting at cos. The DNA terminase genes are under control of a thermosensitive cI repressor. These plasmids lack most of the genes involved in prohead morphogenesis and other head precursors. However, when repression is lifted by destruction of the thermosensitive repressor, the terminase synthesized is able to cut almost 100% of the plasmids. Therefore, these plasmids can mature in the absence of proheads and other head gene products. The plasmids are also able to complement mutants of λ deficient in terminase and DNA maturation. However, in these complementation experiments, if the phage carry mutations in prohead genes E or B, not only is phage DNA maturation blocked, but the plasmid also fails to mature. These experiments show that, in the absence of proheads, phage λ produces a trans-acting inhibitor of maturation. The genetic determinant of this inhibitor maps in a region extending from the middle of gene B to the end of gene C. A model is proposed in which the nicking activity of DNA-bound terminase is inhibited by the trans-acting inhibitor. Prohead (and other factors) binding to this complex would release the block to allow DNA cleavage and packaging.
Protease B of Saccharomyces cerevisiae: Isolation and Regulation of the PRB1 Structural Gene
Authors: Moehle Charles M , Aynardi Martha W , Kolodny Michael R , Park Frances J , Jones Elizabeth W
Published: January 2021

We have isolated the structural gene, PRB1, for the vacuolar protease B of Saccharomyces cerevisiae from a genomic library by complementation of the prb1-1122 mutation. Deletion analysis localized the complementing activity to a 3.2-kilobase pair XhoI-HindIII restriction enzyme fragment. The fragment was used to identify a 2.3-kilobase mRNA. S1 endonuclease mapping indicated that the mRNA and the gene were colinear. No introns were detected. The mRNA is of sufficient size to encode a protein of about 69,000 molecular weight, a number much larger than either the mature enzyme (≃30,000 protein molecular weight) or the sole reported precursor (≃39,000 protein molecular weight). These results suggest that proteolytic processing steps beyond that thought to be catalyzed by protease A may be required to convert the initial glycosylated translation product into mature protease B. The PRB1 mRNA is made in substantial amounts only when the cells have exhausted the glucose supply and enter the diauxic plateau. There is an extended time lag between PRB1 transcription and expression of protease B activity. A deletion that removes about 83% of the coding region was constructed as a diploid heterozygote. Spores bearing the deletion germinate, grow at normal rates into colonies, and have no obvious phenotype beyond protease B deficiency.
First Evidence for Diploidy and Genetic Recombination in Free-Living Amoebae of the Genus Naegleria on the Basis of Electrophoretic Variation
Authors: Cariou Marie Louise , Pernin Pierre
Published: January 2021

Electrophoretic variation for 15 enzyme-coding genes was studied in various Naegleria (Rhizopoda, Vahlkampfiidae) species. The occurrence of complex banding patterns provided the first evidence of a diploid structure of the genome of these amoebae. The putative loci identified were found not to be linked and the genotypic distribution suggested chromosomal recombination for one species (Naegleria lovaniensis).
Evolution under Fertility and Viability Selection
Authors: Nagylaki Thomas
Published: January 2021

Evolution at a single multiallelic locus under arbitrary weak selection on both fertility and viability is investigated. Discrete, nonoverlapping generations are posited for autosomal and X-linked loci in dioecious populations, but monoecious populations are studied in both discrete and continuous time. Mating is random. The results hold after several generations have elapsed. With an error of order s [i.e., O(s)], where s represents the selection intensity, the population evolves in Hardy-Weinberg proportions. Provided the change per generation of the fertilities and viabilities due to their explicit time dependence (if any) is O(s  2), the rate of change of the deviation from Hardy-Weinberg proportions is O(s  2). If the change per generation of the viabilities and genotypic fertilities is smaller than second order [i.e., o(s  2)], then to O(s  2) the rate of change of the mean fitness is equal to the genic variance. The mean fitness is the product of the mean fertility and the mean viability; in dioecious populations, the latter is the unweighted geometric mean of the mean viabilities of the two sexes. Hence, as long as there is significant gene frequency change, the mean fitness increases. If it is the fertilities of matings that change slowly [at rate o(s  2)], the above conclusions apply to a modified mean fitness, defined as the product of the mean viability and the square root of the mean fertility.
STE16, a New Gene Required for Pheromone Production by a Cells of Saccharomyces cerevisiae
Authors: Wilson Katherine L , Herskowitz Ira
Published: January 2021

Genes required for mating by a and α cells of Saccharomyces cerevisiae (STE, "sterile," genes) encode products such as peptide pheromones, pheromone receptors, and proteins responsible for pheromone processing. a-specific STE genes are those required for mating by a cells but not by α cells. To identify new a-specific STE genes, we have employed a novel strategy that enabled us to determine if a ste mutant defective in mating as a is also defective in mating as α without the need to do crosses. This technique involved a strain (K12-14b) of genotype mat  a  1 HML? HMR? sir3ts, which mates as a at 25° and as α at 34°. We screened over 40,000 mutagenized colonies derived from K12-14b and obtained 28 a-specific ste mutants. These strains contained mutations in three known a-specific genes- STE2, STE6 and STE14-and in a new gene, STE16. ste16 mutants are defective in the production of the pheromone, a-factor, and exhibit slow growth. Based on the distribution of a-specific ste mutants described here, we infer that we have identified most if not all nonessential genes that can give rise to a-specific mating defects.
Genetic Transformation of Drosophila melanogaster with an Autonomous P Element: Phenotypic and Molecular Analyses of Long-Established Transformed Lines
Authors: Daniels Stephen B , Clark Stephen H , Kidwell Margaret G , Chovnick Arthur
Published: January 2021

Following transformation of a Drosophila melanogaster true M strain with an autonomous P element, six lines were established and monitored for their molecular and phenotypic properties during a 4-yr period. The number of P elements increased with time in all the lines but the rate of increase differed among lines. Furthermore, degenerate elements arose in each of the lines during propagation. By the end of the 4th yr, the total number of elements in every line was similar to that of a very strong P strain.—At the phenotypic level, all of the transformed lines evolved high P activity, but only three developed complete or nearly complete regulatory ability. The other three lines attained only intermediate levels of regulation over the 4-yr period. One of these lines was particularly noteworthy. Although it contained as many as 55 P elements per genome (20 of which were potentially complete) and had extremely high P activity potential, it continued to exhibit limited regulatory ability. In addition, when females of this line were maintained at high temperatures, the ability to suppress P activity was even further diminished. A strain with this combination of molecular and phenotypic properties, in an apparently stable configuration, has not been previously described.—The results are discussed in the context of the possible role of degenerate elements in regulating P element expression.
Genetic Hitchhiking and the Evolution of Reduced Genetic Activity of the Y Sex Chromosome
Authors: Rice William R
Published: January 2021

A new model for the evolution of reduced genetic activity of the Y sex chromosome is described. The model is based on the process of genetic hitchhiking. It is shown that the Y chromosome can gradually lose its genetic activity due to the fixation of deleterious mutations that are linked with other beneficial genes. Fixation of deleterious Y-linked mutations generates locus-specific selection for dosage tolerance and/or compensation. The hitchhiking effect is most pronounced when operating in combination with an alternative model, Muller's ratchet. It is shown, however, that the genetic hitchhiking mechanism can operate under conditions where Muller's ratchet is ineffective.
Mutations Affecting Expression of the rosy Locus in Drosophila melanogaster
Authors: Lee Chong Sung , Curtis Daniel , McCarron Margaret , Love Carol , Gray Mark , Bender Welcome , Chovnick Arthur
Published: January 2021

The rosy locus in Drosophila melanogaster codes for the enzyme xanthine dehydrogenase (XDH). Previous studies defined a "control element" near the 5′ end of the gene, where variant sites affected the amount of rosy mRNA and protein produced. We have determined the DNA sequence of this region from both genomic and cDNA clones, and from the ry  +10 underproducer strain. This variant strain had many sequence differences, so that the site of the regulatory change could not be fixed. A mutagenesis was also undertaken to isolate new regulatory mutations. We induced 376 new mutations with 1-ethyl-1-nitrosourea (ENU) and screened them to isolate those that reduced the amount of XDH protein produced, but did not change the properties of the enzyme. Genetic mapping was used to find mutations located near the 5′ end of the gene. DNA from each of seven mutants was cloned and sequenced through the 5′ region. Mutant base changes were identified in all seven; they appear to affect splicing and translation of the rosy mRNA. In a related study (T. P. Keith et al. 1987), the genomic and cDNA sequences are extended through the 3′ end of the gene; the combined sequences define the processing pattern of the rosy transcript and predict the amino acid sequence of XDH.
Dosage-Dependent Modifiers of Homoeotic Mutations in Drosophila melanogaster
Authors: Kennison James A , Russell Michael A
Published: January 2021

The determination of segment identity in Drosophila melanogaster appears to be controlled by a small number of genes. In order to identity new components in the process, we have systematically screened the autosomal complement for loci that show a dosage-dependent interaction with mutations in previously characterized genes thought to be important in the determination of segment identity. The dominant homoeotic phenotype of mutations at four loci involved in thoracic leg determination (Pc, Pcl, Antp and Scr) were quantitated in flies bearing a series of synthetic duplications covering more than 99% of the autosomal complement. Twelve regions were identified that when present in three wild-type copies strongly enhanced or suppressed the phenotype of mutations at one or more of the four homoeotic loci examined. The effects of five of these regions appear to correspond to previously described homoeotic loci; the effects of the remaining seven appear to identify new loci involved in the determination of segment identity.
Complete Nucleotide Sequence of the Mouse Lactate Dehydrogenase-A Functional Gene: Comparison of the Exon-Intron Organization of Dehydrogenase Genes
Authors: Fukasawa Kayoko M , Li Steven S-L
Published: January 2021

The complete sequence of 12,851 nucleotides of the mouse lactate dehydrogenase-A (LDH-A) gene has been determined. It includes eight exons, seven introns, promoter and regulatory regions. The B1 repetitive elements present in intron III and VI are oriented in opposite orientation, and they share 72% sequence homology. The exon-intron organization of mouse LDH-Agene is compared with the organizations of other dehydrogenase genes, and the molecular evolution of the nicotinamide adenine dinucleotide binding domains is discussed.
Organ-Specific Expression of Maize Adh1 Is Altered After a Mu Transposon Insertion
Authors: Chen Che-Hong , Oishi Karen K , Kloeckener-Gruissem Barbara , Freeling Michael
Published: January 2021

A new, unstable, organ-specific Adh1 mutant was isolated from a Robertson's mutator line by germinating kernels under partial anaerobic conditions. Families of kernels which showed segregation of a conditional anaerobic lethal phenotype were identified. One mutant, Adh1-3F1124, was shown to express approximately 6% normal levels of ADH1 in seed and anaerobically treated seedlings but expresses normal levels of ADH1 in pollen, the male gametophyte. The ADH1 polypeptide encoded by the mutant allele was found to be indistinguishable from that encoded by the Adh1-3F progenitor but its message levels were lower in seed and seedlings. Robertson's mutator lines are known to carry Mu transposons that cause increased mutation rates. Genomic Southern analysis of Adh1-3F1124 and Adh1-3F showed the presence of a 1.85 kbp insertion at the 5′ region of Adh1. Comparison of the DNA sequences revealed that a Mu1-like element was inserted 31 bp 5′ from the transcriptional start site of Adh1-3F1124gene. The insertion of the Mu element creates an additional TATA box by duplicating the 9 bp genomic sequence—ATATAAATC—at the site of insertion. Consequently, there are two potentially functional TATA sequences, separated by the 1.85 kbp Mu element, 5′ to the transcriptional start site. It is not yet understood how such an arrangement alters the organspecific expression of Adh1.
Chloroplast Genome Evolution in the Genus Avena
Authors: Murai Koji , Tsunewaki Koichiro
Published: January 2021

The genus Avena contains five different chloroplast genomes, I-V. A physical map of chloroplast (ct) DNA of Avena sativa (type I chloroplast genome) was constructed using three restriction endonucleases, PstI, SalI and SmaI. This genome is ca. 135.5 kbp in size, and contains two inverted repeats of ca. 22.5 kbp each, separated by a large (ca. 79.0 kbp) and small (ca. 12.5 kbp) single copy region. The rbcL gene which codes for the large subunit of ribulose 1,5-bisphosphate carboxylase, was located in the map. Restriction fragment patterns of all five chloroplast genomes were compared, and among them five fragment size and five restriction site mutations were disclosed. Four site mutations were found in two or more chloroplast genomes, the other site and five fragment size mutations were specific to one or another of the chloroplast genomes. A dendrogram showing phylogenetic relationships among the five chloroplast genomes, based on the distribution of the common and specific mutations among them, indicates that chloroplast genome divergence characterized by three restriction site mutations occurred first between two diploid groups, each carrying A and C genome (nuclear), respectively, followed by further speciation in each group.
Nucleo-Cytoplasmic Interaction During Macronuclear Differentiation in Ciliate Protists: Genetic Basis for Cytoplasmic Control of SerH Expression During Macronuclear Development in Tetrahymena thermophila
Authors: Doerder F P , Berkowitz M S
Published: January 2021

A novel class of mutations affecting the developmental expression of SerH cell surface antigen genes of Tetrahymena thermophila is described. Unlike previous categories of mutation, the four independently isolated mutations of this class act through the cytoplasm to affect SerH genes during macronuclear development. That is, macronuclei which develop under the influence of mutant cytoplasm do not subsequently express H, most likely because the developmental processing of SerH genes is affected. The cytoplasmic effect is specific for the SerH locus and is independent of which SerH allele is present. In place of H, hitherto unknown antigens are expressed. Expression of SerH can be rescued during development either by wild-type cytoplasm exchanged between conjugants or by the homozygous wild-type genotype. The mutations segregate independently of the SerH genes and identify one, possibly two, bistable genes. Possible models to explain these results are discussed.
Genetic Diversity in Cellular Slime Molds: Allozyme Electrophoresis and a Monoclonal Antibody Reveal Cryptic Species Among Dictyostelium discoideum Strains
Authors: Briscoe David A , Gooley Andrew A , Bernstein R L , McKay George M , Williams Keith L
Published: January 2021

Cellular slime molds have been classified on the basis of a small number of descriptive criteria such as fruiting body color and morphology, and, in heterothallic species, by assignment to compatible mating groups. However, some isolates which are morphologically classified as conspecific do not fall into a simple mating-type classification; for example some are asexual or homothallic. An increasing interest in inter-strain genetic variation in studies of development and simple behavior has led us to reassess genetic relationships among a number of frequently used isolates. Allozyme electrophoresis of 16 soluble enzymes and use of a monoclonal antibody show that there is relatively little genetic diversity among sexually competent Dictyostelium discoideum isolates, despite considerable variation in geographic origin and time since isolation in the laboratory. In contrast a pair of asexual strains and each of two homothallic strains are genetically quite distinct and differ sufficiently from each other, and from sexually competent isolates, to warrant their recognition as separate species. There are probably four biological species represented in the supposedly D. discoideum isolates studied. This heterogeneity extends to other cellular slime mold species. Each of three isolates of Dictyostelium purpureum is genetically distinct from the others. Limited analysis of other cellular slime molds indicates that the generic distinction of Dictyostelium and Polysphondylium must be questioned. This study emphasizes that caution should be applied in classifying simple organisms on morphological criteria.
Isolation and Characterization of a 1.7-kb Transposable Element from a Mutator Line of Maize
Authors: Taylor Loverine P , Walbot Virginia
Published: January 2021

We have cloned and sequenced a 1.7-kb Mu element from a Mutator line of maize and compared its structure to Mu1, a 1.4-kb element. With the exception of a 385-bp block of DNA present in the 1.7-kb element, these transposable elements are structurally similar, sharing terminally inverted and internal direct repeated sequences. Derivation of 1.4-kb elements from the 1.7-kb class via deletion of internal sequence is suggested by the finding that a portion of the extra DNA in Mu1.7 is part of a truncated direct repeat sequence in the 1.4-kb element. An abundant poly(A)+ RNA homologous to a portion of this extra DNA is present in several tissues of both Mutator and non-Mutator lines. Analysis of transcripts from an unstable mutant bronze1 (bz) allele containing a Mu1.7 element inserted in an exon of the gene detects three species of poly(A)+ RNA that hybridize to a Bz1 (Bronze) gene probe: the largest contains the entire Mu1.7 element in the Bz1 gene transcript; another appears to be a spliced, chimeric transcript; the smallest is normal size Bz1 mRNA. The latter is most likely encoded by the normal-size alleles detected by Southern analysis of tissue expressing purple pigment, suggesting that normal gene function is restored by excision of the Mu1.7 element.
Interaction of Endosperm Size Factors in Maize
Authors: Birchler James A , Hart Jennifer R
Published: January 2021

Crosses involving certain B-A translocations produce a reduced size of endosperm when those regions of the A chromosomes are missing in the sperm that fertilizes the polar nuclei. Previous studies involving the long arm of chromosome 10 showed that additional copies of this segment introduced through the maternal side could not rescue the reduced size phenotype conditioned by the corresponding deficiency in the paternal gamete. In this paper, experiments are described showing that other segments introduced maternally produce an even smaller kernel when fertilized by a sperm missing the same A chromosome segment or other ones that carry factors affecting endosperm size.—The example analyzed in detail involves reciprocal crosses between TB-4Sa and TB-10L19. Extra doses of 4S enhance the small kernel effect normally produced by TB-10L19. The additional copies of 4S have no effect on kernel mass when the 10L segment is present in the paternal contribution to the endosperm. The maternal enhancement by 4S is also effective with crosses by TB-1La but not by TB-1Sb. A survey of inter se crosses of B-A translocations shows that, when the maternal enhancement occurs, it is confined to those regions that themselves give a small kernel effect when used as a male. This correlation is strengthened by the observations that TB-10L19 enhances the small kernel effect of TB-1Sb, but TB-10L32 will not. Since these two B-10L translocations span the best localized small kernel effect region, this result supports the correlation of maternal enhancement regions with the paternal small kernel effect ones.—Because the enhancement can be attributed to a dosage effect and because the enhancement regions are coincident with the small kernel segments, it is postulated that this interacting system is analogous to aneuploid effects in diploid tissues but exhibits unique properties because of the evolutionary history and triploid condition of the endosperm.
A New Non-Mendelian Genetic Element of Yeast That Increases Cytopathology Produced by M1 Double-Stranded RNA in ski Strains
Authors: Esteban Rosa , Wickner Reed B
Published: January 2021

The Saccharomyces cerevisiae SKI (superkiller) genes are repressors of replication of M, L-A, and L-BC double-stranded (ds) RNAs; ski strains have an increased M dsRNA copy number and, as a result, are cold-sensitive for growth at 8°. Growth is normal, however, at higher temperatures. We have found a new cytoplasmic genetic element [D] (for disease) that makes M1 dsRNA-containing superkiller strains grow slowly at 30°, not at all at 37°, and only very poorly at 20°. These growth defects require three factors: a chromosomal ski mutation, the presence of M1 dsRNA, and the presence of the new cytoplasmic factor, [D]. We have isolated mutants unable to ma intain [D] (mad), at least one of which is due to mutation of a single chromosomal locus. Further, [D] can be cured by growth at 37-39°. We present evidence that [D] is not M, L-A, L-BC or W dsRNAs or mitochondrial DNA, 2µ DNA, or [psi], but [D] depends on L-A for its maintenance. We also show that [D] is distinct from [B], a cytoplasmic element that allows M1 dsRNA to be stably replicated and maintained in spite of defects in certain chromosomal MAK genes that would otherwise be necessary. [D] activity is blocked by the presence of another extrachromosomal element, called [DIN] (for [D] interference). [D] and [DIN] may be different natural variants of the same molecule.
Proposed Mechanism of Inheritance and Expression of the Human Fragile-X Syndrome of Mental Retardation
Authors: Laird Charles D
Published: January 2021

A mechanism is proposed for the inheritance and expression of the fragile-X-linked syndrome of mental retardation in humans. Two independent events are required for expression of the syndrome: the fragile-X mutation, and X chromosome inactivation in pre-oogonial cells. The fragile-X mutation at site Xq27 has little or no effect until the chromosome is inactivated in a female as part of the process of dosage compensation. At a stage where the inactivated X chromosome would normally be reactivated in preparation for oogenesis, the mutation results in a local block to the reactivation process. This block to reactivation leads to mental retardation in progeny by reducing the level of products from the unreactivated Xq27 region in male cells, and, for a heterozygous female, in somatic cells in which the normal X chromosome has been inactivated. Published data relevant to this proposed mechanism are discussed.
Evidence for Related Functions of the RNA Genes of Saccharomyces cerevisiae
Authors: Last Robert L , Maddock Janine R , Woolford John L
Published: January 2021

The yeast genes RNA2-RNA11 are necessary for splicing of nuclear intron-containing pre-mRNAs. We investigated the relationships among these genes by asking whether increased expression of one RNA gene leads to suppression of the temperature-sensitive lethality of a mutation in any other RNA gene. The presence of extra plasmid-borne copies of the RNA3 gene relieves the lethality of temperature-sensitive rna4 mutations. A region of the yeast genome (SRN2) is described that suppresses temperature-sensitive rna2 mutations when it is present on either medium or high-copy number plasmids. Neither suppression occurs via a bypass of RNA gene function since null alleles of rna2 and rna4 are not suppressed by elevated dosage of SRN2 and RNA3, respectively. These results suggest that the SRN2 and RNA2 gene products have related functions, as do the RNA3 and RNA4 gene products.
Characterization of X-linked recessive lethal mutations affecting embryonic morphogenesis in Drosophila melanogaster.
Authors: Eberl D F , Hilliker A J
Published: January 2021

This study attempted to assay the zygotic contribution of X chromosome genes to the genetic control of embryonic morphogenesis in Drosophila melanogaster. A systematic screen for X-linked genes which affect the morphology of the embryo was undertaken, employing the phenotype of whole mount embryos as the major screening criterion. Of 800 EMS-induced lethal mutations analyzed, only 14% were embryonic lethal, and of these only a minority affected embryonic morphogenesis. By recombination and complementation analyses, the mutations that affected embryonic morphogenesis were sequestered into 26 complementation groups. Fourteen of the loci correspond to genes previously identified in a large-scale screen in which fixed cuticles were examined, and 12 new loci have been identified. Most of the mutations which disrupt embryonic morphology had specific and uniform mutant phenotypes. Mutations were recovered which disrupt major morphogenetic events such as gastrulation, germ band retraction and head involution. No mutations were found which arrest the embryos prior to blastoderm formation. However, a novel class was found, one comprised of mutations which interfere with the development of internal structures but not cuticular structures. Nevertheless, saturation of the X chromosome for genes important for embryonic morphogenesis is probably incomplete.
Mutants resistant to anti-microtubule herbicides map to a locus on the uni linkage group in Chlamydomonas reinhardtii.
Authors: James S W , Ranum L P , Silflow C D , Lefebvre P A
Published: January 2021

We have used genetic analysis to study the mode of action of two anti-microtubule herbicides, amiprophos-methyl (APM) and oryzalin (ORY). Over 200 resistant mutants were selected by growth on APM- or ORY-containing plates. The 21 independently isolated mutants examined in this study are 3- to 8-fold resistant to APM and are strongly cross-resistant to ORY and butamiphos, a close analog of APM. Two Mendelian genes, apm1 and apm2, are defined by linkage and complementation analysis. There are 20 alleles of apm1 and one temperature-sensitive lethal (33 degrees) allele of apm2. Mapping by two-factor crosses places apm1 6.5 cM centromere proximal to uni1 and within 4 cM of pf7 on the uni linkage group, a genetically circular linkage group comprising genes which affect flagellar assembly or function; apm2 maps near the centromere of linkage group VIII. Allele-specific synthetic lethality is observed in crosses between apm2 and alleles of apm1. Also, self crosses of apm2 are zygotic lethal, whereas crosses of nine apm1 alleles inter se result in normal germination and tetrad viability. The mutants are recessive to their wild-type alleles but doubly heterozygous diploids (apm1 +/+ apm2) made with apm2 and any of 15 apm1 alleles display partial intergenic noncomplementation, expressed as intermediate resistance. Diploids homozygous for mutant alleles of apm1 are 4-6-fold resistant to APM and ORY; diploids homozygous for apm2 are ts- and 2-fold resistant to the herbicides. Doubly heterozygous diploids complement the ts- phenotype of apM2, but they are typically 1.5-2-fold resistant to APM and ORY. From the results described we suggest that the gene products of apm1 and apm2 may interact directly or function in the same structure or process.
An in vitro assay for frameshift mutations: hotspots for deletions of 1 bp by Klenow-fragment polymerase share a consensus DNA sequence.
Authors: de Boer J G , Ripley L S
Published: January 2021

The fidelity of in vitro DNA synthesis catalyzed by the large fragment of DNA polymerase I was examined. The templates, specifically designed to detect shifts to the +1 or to the -1 reading frame, are composites of M13mp8 and bacteriophage T4 rIIB DNA and were designed to assist in the identification of the types of frameshifts that are the specific consequence of DNA polymerization errors. In vitro polymerization by the Klenow fragment produced only deletions, rather than the mixture of duplications and deletions characteristic of in vivo frameshifts. The most frequent frameshifts were deletions of 1 bp opposite a template purine base. Hotspots for these deletions occurred when the template purine immediately preceded the template sequence TT. The highest mutation frequencies were seen when the TTPu consensus sequence was adjacent to G:C rich sequences in the 3' direction. The nature of the consensus sequence itself distinguishes this 1-bp deletion mechanism from those operating in DNA repeats and attributed to the misalignment of DNA primers during synthesis. Deletions that were larger than 1 or 2 bp isolated after in vitro replication were consistent with the misalignment of the primer. Deletions of 2 bp and complex frameshifts (the replacement of AA by C) were also found. Mechanisms that may account for these mutations are discussed.
Isolation and analysis of a novel class of suppressor of Ty insertion mutations in Saccharomyces cerevisiae.
Authors: Fassler J S , Winston F
Published: January 2021

Using a new scheme for the isolation of suppressor of Ty insertion mutations (spt mutations) in yeast, we have identified six new SPT genes. Mutations in two of these genes, SPT13 and SPT14, exhibit a novel suppression pattern: suppression of complete Ty insertion mutations, but not of solo delta insertion mutations. Transcriptional analysis shows that spt13- and spt14-mediated suppression of Ty insertion mutations is the result of an elevation in the levels of adjacent gene transcription. In spite of the failure of these mutations to suppress solo delta insertion mutations, they do cause changes in transcription of at least one solo delta insertion mutation. In addition, spt13 and spt14 mutations are epistatic to mutations in certain other SPT genes that do suppress solo delta insertion mutations. These results suggest that the SPT13 and SPT14 gene products may act via sequences in both the delta and epsilon regions of Ty elements. Finally, mutations in SPT13 cause sporulation and mating defects and SPT14 is essential for growth, suggesting that these two genes have important roles in general cellular functions.
hph-1: a mouse mutant with hereditary hyperphenylalaninemia induced by ethylnitrosourea mutagenesis.
Authors: Bode V C , McDonald J D , Guenet J L , Simon D
Published: January 2021

Ethylnitrosourea mutagenesis of spermatogonial stem cells and a three-generation breeding scheme were used to screen for recessive mutations that cause defects in phenylalanine metabolism leading to elevated serum levels of this amino acid. This paper describes the isolation of such a mutation, hph-1, causing a heritable hyperphenylalaninemia in the neonate and weanling and an inability to effectively clear a phenylalanine challenge in the adult. Micro-pedigree analysis of the original mutant mouse and data obtained from crosses of affected and unaffected animals indicate that the mutation segregates in an autosomal recessive manner. An interspecies mouse backcross mapping experiment places the mutant gene locus on mouse chromosome 14 very near Np-1 and a backcross experiment with a conventional inbred mouse strain involving a nearby locus confirms the chromosome 14 assignment. The initial symptomatology of the mutant phenotype suggests this mutant may represent a useful animal model for the study of hyperphenylalaninemia in man.
Intraspecific variation and multicircularity in Brassica mitochondrial DNAs.
Authors: Palmer J D
Published: January 2021

Intraspecific variation was examined among 25 mitochondrial DNAs (mtDNAs), representing between two and five lines of eight agriculturally important Brassica species. Each of the approximately 140 restriction sites surveyed was invariant within each species. Only two length polymorphisms, deletions of 700 bp and 100 bp in a Brassica nigra line, were detected. A single inversion polymorphism was found; this distinguished two different mtDNA populations within a single line of Brassica hirta. Approximately 60% of the mtDNA molecules in this line and in two other B. hirta lines were identical, whereas the other 40% of the molecules in the first line differed by a 62-kb inversion. Levels of within-species variability in mtDNA appear to be lower in Brassica than in other groups of plants. These mtDNA comparisons are in agreement with cpDNA studies regarding the maternal ancestry of three amphidiploid Brassica species. This agreement and others imply that the two cytoplasmic genomes must have shared a common, maternal mode of transmission throughout the history of the genus. Finally, analysis of a supercoiled fraction of mtDNA from cauliflower (Brassica oleracea) provides the strongest evidence yet in support of the multicircular model for plant mtDNAs.
Molecular analysis of the neurogenic locus mastermind of Drosophila melanogaster.
Authors: Yedvobnick B , Smoller D , Young P , Mills D
Published: January 2021

The neurogenic loci comprise a small group of genes which are required for proper division between the neural and epidermal pathways of differentiation within the neuroectoderm. Loss of neurogenic gene function results in the misrouting of prospective epidermal cells into neuroblasts. A molecular analysis of the neurogenic locus mastermind (mam) has been initiated through transposon tagging with P elements. Employing the Harwich strain as the source of P in a hybrid dysgenesis screen, 6000 chromosomes were tested for the production of lethal mam alleles and eight mutations were isolated. The mam region is the site of residence of a P element in Harwich which forms the focus of a chromosome breakage hotspot. Hybrid dysgenic induced mam alleles elicit cuticular and neural abnormalities typical of the neurogenic phenotype, and in five of the eight cases the mutants appear to retain a P element in the cytogenetic region (50CD) of mam. Utilizing P element sequence as probe, mam region genomic DNA was cloned and used to initiate a chromosome walk extending over 120 kb. The physical breakpoints associated with the hybrid dysgenic alleles fall within a 60-kb genomic segment, predicting this as the minimal size of the mam locus barring position effects. The locus contains a high density of repeated elements of two classes; opa (CAX)n and (dC-dA)n.(dG-dT)n. A preliminary study of the transcriptional activity of the mam region is presented.
Parentage analysis with genetic markers in natural populations. I. The expected proportion of offspring with unambiguous paternity.
Authors: Chakraborty R , Meagher T R , Smouse P E
Published: January 2021

Recent studies indicate that polymorphic genetic markers are potentially helpful in resolving genealogical relationships among individuals in a natural population. Genetic data provide opportunities for paternity exclusion when genotypic incompatibilities are observed among individuals, and the present investigation examines the resolving power of genetic markers in unambiguous positive determination of paternity. Under the assumption that the mother for each offspring in a population is unambiguously known, an analytical expression for the fraction of males excluded from paternity is derived for the case where males and females may be derived from two different gene pools. This theoretical formulation can also be used to predict the fraction of births for each of which all but one male can be excluded from paternity. We show that even when the average probability of exclusion approaches unity, a substantial fraction of births yield equivocal mother-father-offspring determinations. The number of loci needed to increase the frequency of unambiguous determinations to a high level is beyond the scope of current electrophoretic studies in most species. Applications of this theory to electrophoretic data on Chamaelirium luteum (L.) shows that in 2255 offspring derived from 273 males and 70 females, only 57 triplets could be unequivocally determined with eight polymorphic protein loci, even though the average combined exclusionary power of these loci was 73%. The distribution of potentially compatible male parents, based on multilocus genotypes, was reasonably well predicted from the allele frequency data available for these loci. We demonstrate that genetic paternity analysis in natural populations cannot be reliably based on exclusionary principles alone. In order to measure the reproductive contributions of individuals in natural populations, more elaborate likelihood principles must be deployed.
Nuclear migration and mitochondrial inheritance in the mushroom agaricus bitorquis.
Authors: Hintz W , Anderson J B , Horgen P A
Published: January 2021

Mitochondrial (mt) DNA restriction fragment length polymorphisms (RFLPs) were used as genetic markers for following mitochondrial inheritance in the mushroom Agaricus bitorquis. In many basidiomycetes, bilateral nuclear migration between paired homokaryotic mycelia gives rise to two discrete dikaryons which have identical nuclei but different cytoplasms. Although nuclear migration is rare in A. bitorquis, unidirectional nuclear migration occurred when a nuclear donating strain (8-1), was paired with a nuclear recipient strain (34-2). The dikaryon recovered over the nuclear recipient mate (Dik D) contained nuclei from both parents but only mitochondria from the recipient mate; thus nuclei of 8-1, but not mitochondria, migrated through the resident hyphae of 34-2 following hyphal anastomosis. The two mitochondrial types present in a dikaryon recovered at the junction of the two cultures (Dik A) segregated during vegetative growth. Dikaryotic cells having the 34-2 mitochondrial type grew faster than cells with the 8-1 mitochondrial type. Fruitbodies, derived from a mixed population of cells having the same nuclear components but different cytoplasms, were chimeric for mitochondrial type. The transmission of mitochondria was biased in favor of the 8-1 type in the spore progeny of the chimeric fruitbody. Protoplasts of dikaryon (Dik D), which contained both nuclear types but only the 34-2 mitochondrial type, were regenerated and homokaryons containing the 8-1 nuclear type and the 34-2 mitochondrial type were recovered.
The unc-22(IV) region of Caenorhabditis elegans: genetic analysis of lethal mutations.
Authors: Clark D V , Rogalski T M , Donati L M , Baillie D L
Published: January 2021

The organization of essential genes in the unc-22 region, defined by the deficiency sDf2 on linkage group IV, has been studied. Using the balancer nT1 (IV;V), which suppresses recombination over 49 map units, 294 lethal mutations on LGIV(right) and LGV(left) were recovered using EMS mutagenesis. Twenty-six of these mutations fell into the unc-22 region. Together with previously isolated lethal mutations, there is now a total of 63 lethal mutations which fall into 31 complementation groups. Mutations were positioned on the map using eight overlapping deficiencies in addition to sDf2. The lethal alleles and deficiencies in the unc-22 region were characterized with respect to their terminal phenotypes. Mapping of these lethal mutations shows that sDf2 deletes a minimum of 1.8 map units and a maximum of 2.5 map units. A minimum estimate of essential gene number for the region using a truncated Poisson calculation is 48. The data indicate a minimum estimate of approximately 3500 essential genes in the Caenorhabditis elegans genome.
Molecular genetics of serine and threonine catabolism in Saccharomyces cerevisiae.
Authors: Petersen J G , Kielland-Brandt M C , Nilsson-Tillgren T , Bornaes C , Holmberg S
Published: January 2021

The catabolic L-serine (L-threonine) deaminase of Saccharomyces cerevisiae allows the yeast to grow on media with L-serine or L-threonine as sole nitrogen source. A mutant, cha1 (catabolism of hydroxyamino acids), lacking this enzyme activity has been isolated. We have cloned the CHA1 gene by complementation of a cha1 mutation. Northern analysis showed that CHA1 mRNA has a size of about 1200 ribonucleotides. CHA1 is probably the structural gene for the enzyme; it is an abundant RNA in cells grown with serine and threonine as nitrogen source, whereas it is not detected when cells are grown on ammonium or proline, i.e., the transcription of the CHA1 gene is induced by serine or threonine. Under induced growth conditions haploid ilv1 CHA1 strains do not require isoleucine, i.e., the catabolic deaminase is able to substitute for the biosynthetic threnonine deaminase encoded by the ILV1 gene. We have identified a nuclear, recessive mutation, sil1, that suppresses ilv1 mutations by increased transcription of the CHA1 gene under growth conditions leading to partial induction. The sil1 mutation could exert its effect by increasing the effective pools of the hydroxyamino acids. Alternatively SIL1 may encode a negatively acting regulatory protein for CHA1.
Assessment of pleiotropic effects of a gene substitution in pea by two-dimensional polyacrylamide gel electrophoresis.
Authors: Gottlieb L D , de Vienne D
Published: January 2021

We examined, by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), near-isogenic lines of the r-gene in pea (Pisum sativum) which determines round (RR) vs. wrinkled (rr) seed. The study was undertaken to assess the number of protein changes resulting from a single gene substitution as a means of quantifying pleiotropic effects. A total of 636 to 770 resolvable polypeptides were identical in all respects between RR and rr for roots, shoots, leaflets, stipules, young ovaries, and young embryos. A single difference between the lines became evident about 21-23 days after anthesis in the embryos. Mature seeds of the two lines showed 62 spot differences in addition to differences in four clusters of spots, representing about 10% of the total number of spots visible on the gels. The protein differences are presumably involved in the many known physiological differences of the two seed types. 2-D PAGE analyses of near-isogenic lines are likely to be valuable in a number of quantitative and developmental genetic contexts.