Insertional disruption of the nusB (ssyB) gene leads to cold-sensitive growth of Escherichia coli and suppression of the secY24 mutation

Summary The Escherichia coli gene ssyB was cloned and sequenced. The ssyB63 (Cs) mutation is an insertion mutation in nusB, while the nusB5 (Cs) mutation suppresses secY24, indicating that inactivation of nusB causes cold-sensitive cell growth as well as phenotypic suppression of secY24. The correct map position of nusB is 9.5 min rather than I I min as previously assigned. It is located at the distal end of an operon that contains a gene showing significant homology with a Bacillus subtilis gene involved in riboflavin biosynthesis.     

Protoclonal variation of plant regeneration in rice

Protoplasts were isolated from callus derived from a single homozygous seed of Oryza sativa L. var. Norin 8. Thirty protoclones were randomly selected and these showed variation in regeneration frequency ranging from 0–87% with an average of 52%. The potential for regeneration of each protoclone as reflected in the regeneration frequency was analyzed five times over a period of 250 days and showed that the protoclones can be classified into three types, namely: protoclones with high regeneration frequency; protoclones with low regeneration frequency, both of which maintained their respective levels of regeneration potential; and protoclones with gradually decreasing regeneration frequency. Secondary protoclones established from protoplasts isolated from some of these protoclones and regenerated 2–3 times for a period of 120 days also showed further reduction in regeneration frequency. The polypeptide composition analyzed by two dimensional gel electrophoresis suggests the presence of specific polypeptides related to regeneration potential. Analysis of ploidy level based on plant morphology and pollen size suggests the predominance of tetraploids among the regenerated plants.     

Substructural morphogenesis of the spindle apparatus in meiotic basidia ofCoprinus micaceus (Agaricales)

The spindle apparatus ofCoprinus micaceus begins to develop from the diglobular polar body outside the nucleus. During both meiotic divisions it operates inside the nuclear envelope and consists of two amorphous poles, a central bundle of interpolar microtubules, and chromosomal microtubules. A metaphase plate cannot exist because the interpolar strand of fibers is persistent throughout the division process. Within the spindle axis more than 100 microtubules can be estimated. They are encircled by a ring of chromatic structures. During the telophase the former spindle pole is evaginated from the nuclear envelope and contacts the plasmalemma near the cell wall.     

Homoeosis in Drosophila: Evidence for a maternal effect of the polycomb locus

When heterozygous, dominant mutant alleles of the Polycomb locus are associated with a variety of adult homoeotic effects. Zygotes homozygous for these alleles die as late embryos showing homoeotic transformation of head, thoracic, and abdominal segments. This study shows that embryos homozygous for Pc³ are more extreme than those homozygous for Pc¹ or Pc². Moreover, Pc¹/Pc³ heterozygotes are more extensively transformed if their mothers were Pc³/ + than if they were Pc¹/ +; this effect does not depend on zygotic genetic background and must be maternal in nature. Embryos homozygous for Pc³ are less extreme if they arise from Pc³/ + / + than from Pc³/ + mothers. These results strongly suggest that the Polycomb locus acts maternally as well as zygotically to affect early determinative decisions.     

The mutagenic potency of 1,8-dinitropyrene in cultured mouse lymphoma cells

Although non-toxic, 1,8-dinitropyrene (1,8-DNP) was mutagenic for mouse lymphoma L5178Y cells when assayed for induced resistance to 6-thioguanine, methotrexate, ouabain and 1-β-D-arabinofuranosyl cytosine. In bacteria, nitropyrenes are potent inducers of frame-shift mutations, and the induction of ouabain-resistant mutants, believed to be due to base-pair substitutions, suggests that the mechanism of action may be different in mouse cells and bacteria. Long treatment times were required to detect 1,8-DNP-induced mutants in L5178Y cells, suggesting the possibility of an inducible activation system. 4-Nitroquinoline 1-oxide was both toxic and mutagenic to these same 4 mutation assays after short (2 h) treatment times. The dilemma that exists when comparing the mutagenic potential of test chemicals when concentration of mutagen, treatment times and toxicity are markedly different, is discussed.     

Occurrence of resistance to neomycin and kanamycin in Bacillus popilliae and certain serotypes of Bacillus thuringiensis: Mutation potential in sensitive strains

Serotypes of Bacillus thuringiensis and the commercial strain of Bacillus popilliae were examined for their inherent resistance to antibiotics and their mutation potential in respect to neomycin and kanamycin, the presence of which would preclude the use of plasmids marked by genes for resistance to the antibiotics. Clones on initial plates were detected by the recurrence of resistance colonies at superimposable sites on serial replicaplates containing the antibiotic. Susceptible strains were selected for the determination of their antibiotic-resistance mutation potential. Three varieties of B. thuringiensis were found to be doubly resistant, seven varieties were singly resistant (Neo^r), and three other varieties, including B. popilliae, were susceptible to both antibiotics. Estimates of mutation ratios revealed that three serotypes developed no resistant mutants to either antibiotics in populations as high as 3.0 × 10¹⁰; seven other serotypes developed no resistance to kanamycin in populations as high as 4.6 × 10⁹ cells. Three other serotypes exhibited mutation ratios as high as 1.6 × 10^?2. We were unable to determine the mutation ratio for B. popilliae.     

Was globin evolution very rapid in its early stages?: A dubious case against the rate-constancy hypothesis

Summary Goodman et al's (1975) claim of accelerated evolution in the early stages of globin evolution is based on an erroneous assignment of the time of divergence of vertebrate myoglobin and hemoglobin. When this is corrected, there is no basis for their claim. The data are much more consistent with the nearly constant rate expected on the neutral mutation-random drift hypothesis than with the uneven rates expected if most amino acid changes were caused by substitution of favorable mutants through Darwinian selection. In addition, the majority of the codons determined by their maximum parsimony method have turned out to be wrong when compared to the actual nucleotide sequences of rabbit and human hemoglobins determined by direct sequencing.Contribution No. 1314 from the National Institute of Genetics, Mishima, 411 Japan.     

Isolation of recombinant plasmids and phage carrying the lexA gene of Escherichia coli K-12

The lexA gene of Escherichia coli K-12 was cloned from the plasmid pLC44-14 into pBR322. Plasmids carrying lexA+ were selected by their ability to complement a recessive tsl mutation, which is believed to be a mutation in lexA. The smallest lexA+ recombinant plasmid, pJL21, contained an EcoRI-PstI fragment 2.9 kilobases (kb) in length; two larger plasmids also contained this fragment, and genetic material to one or both sides of the EcoRI-PstI fragment. Plasmids homologous to pJL21, but carrying a dominant mutation, lexA3, or one of three recessive amber mutations in lexA, termed spr, were also isolated. To clone the EcoRI-PstI fragment onto a lambda vector, the PstI end was first converted to an EcoRI end by attachment of a 100-base pair PstI-EcoRI fragment isolated from the plasmid ColE1; the resultant EcoRI fragment was then cloned into the lambda vector lambda gt4. A restriction map of pLC44-14 was obtained for nine restriction enzymes. The orientation of this map was determined relative to the E. coli genetic map by complementation of the gene ubiA+ and by comparison with restriction enzyme digests of another plasmid, pLC11-9, which carries dnaB, a gene closely linked to lexA, but does not carry lexA.     

Induction,ultrastructure, isolation,and tissue culture of chlorophyll mutants in carrot

Summary Seeds ofDaucus carota “Danvers” were treated with ethyl methanesulfonate (EMS) for 6-hr periods at concentrations of 0.01, 0.03, 0.1, 0.3, 1.0, and 3.0% to induce plastid mutants. In these treatments, there was a gradual decrease in percent germination from control up to 1.0% EMS and no germinations at 3.0%. The number of chlorophyll mutants increased with dose of mutagen. One mutant plant was isolated from the 0.1% treatment and it had leaf sections of green, white layered on green and pure white; and white and green striped petioles. Histogenic analysis of this mutant showed it to be a GGW chimera, the “all-white” sectors being GWW, arising from displacement of L-II by L-III. Electron micrographs of the white sections showed plastids that had dilated thylakoids typical of PS-I mutants. So called “mixed cells” of normal and mutant plastids were found, suggesting a plastome mutation. Leaf and petiole sections have been successfully cultured through the development of callus, and both green and white plants have been regenerated. Regenerated white plantlets were insensitive to 10 mM methyl viologen (paraquat), whereas green tissues were killed by the herbicide. Support for some of this work was provided by the Miami University Faculty Research Committee and the Comprehensive Employment and Training Act (CETA). This paper will be included as part of the dissertation work of P. D. Miller.     

Thermo-inducible expression of cloned early genes of bacteriophage Mu.

An EcoRI fragment, containing approx. 5100 base pairs (bp) of the immunity-end of bacteriophage Mu, was inserted into the multicopy plasmid pMB9 by in vitro recombination. The expression of early Mu genes, located on the cloned fragment, is thermo-inducible because of the presence of the ts mutation in gene c. The isolation of a transformant harbouring the recombinant plasmid, pGP1, was possible only when expression of Mu genes was prevented. pGP1 can be maintained at 28 degrees C at high copy number, but at 42 degrees C the pGP1 containing cells are killed due to the expression of the kil gene of Mu. The following Mu genes are present on pGP1: the ner gene, the integration and replication genes A and B, the cim gene, and the kil gene. pGP1 containing cells do not show Gam and Sot activity at 42 degrees C, therefore the leftmost EcoRI site on the Mu DNA is located between genes kil and gam or sot, or within the gam or sot gene.