Conserved organization of an avian histone gene cluster with inverted duplications of H3 and H4 genes

Summary The organization of histone gene clusters of the duckCairina moschata was studied in the DNA inserts of two recombinant phage that overlap and feature identical histone gene arrangements but differ in sequence details and in the extent of repetition of an AT-rich motif in one of the nontranscribed spacer regions. These few but substantial differences between otherwise nearly identical histone gene groups suggest that we have independently isolated alleles of the same site of the duck genome or that this gene arrangement occurs (with slight variations) more than once per haploid genome. Within the histone gene cluster described, H3 and H4 genes are duplicated (with inverted orientation), whereas one H1 gene is flanked by single H2A and H2B genes. The arrangement of duck histone genes described here is identical to a subsection of the chicken genome but differs from any other published histone gene cluster.     

DNA microenvironments and the molecular clock

Summary A few years ago we presented a stationary Markov model of gene evolution according to which only homologous genes from not too divergent species obeying the condition of being stationary may behave as reliable molecular clocks. A compartmentalized model of the nuclear genome in which the genes are distributed in compartments, the isochores, defined by their G+C content has been proposed recently. We have found that only homologous gene pairs that are stationary, and belong to the same isochore, can be used consistently for the determination of phylogeny and base substitution rate. In particular, for the rodent-human couple, only about half of the homologous gene pairs are stationary. Stationary genes evolve at the third silent codon position with the same velocity independent of the genes and base composition. By contrast, nonstationary genes display apparent rate values (pseudovelocities) that are significantly higher. Our results cast doubt upon recent claims of a large acceleration in the rate of molecular evolution in rodents.     

Vectors permitting visual monitoring of simple transposition events

The construction and use of two novel transposon(Tn)-delivery vectors is described. These vectors carry Inc.W or Inc.N broad-host-range transfer functions cloned next to the narrow-host-range replicon of pBR329. The host specificities of pSLX10 and pSLX23 both complement and extend the host specificities of existing Tn delivery vectors. Plasmids pSLX10 and pSLX23 were shown to transfer at high frequency in intergeneric matings. The lux genes which are present on each vector permit the visual monitoring of transconjugants which have retained a Tn element, but are devoid of plasmid molecules. pSLX10 and pLSX23 were efficiently used to generate a range of auxotrophic mutants in various strains of Pseudomonas as well as to clone genes from Serratia liquefaciens. These vectors may have general applicability to identify and clone genes in a wide range of Gram-negative bacteria.     

Cloning and sequencing the genes encoding uptake-hydrogenase subunits of Rhodocyclus gelatinosus

Summary Rhodocyclus gelatinosus grew photosynthetically in the light and consumed H₂ at a rate of about 665 nmol/min per mg protein. The uptake-hydrogenase (H₂ase) was found to be membrane bound and insensitive to inhibition by CO. The structural genes of R. gelatinosus uptake-H₂ase were isolated from a 40 kb cosmid gene library of R. gelatinosus DNA by hybridization with the structural genes of uptake-H₂ase of Bradyrhizobium japonicum and Rhodobacter capsulatus. The R. gelatinosus genes were localized on two overlapping DNA restriction fragments subcloned into pUC18. Two open reading frames (ORF1 and ORF2) were observed. ORF1 contained 1080 nucleotides and encoded a 39.4 kDa protein. ORF2 had 1854 nucleotides and encoded a 68.5 kDa protein. Amino acid sequence analysis suggested that ORF1 and ORF2 corresponded to the small (HupS) and large (HupL) subunits, respectively, of R. gelatinosus uptake-H₂ase. ORF1 was approximately 80% homologous with the small, and ORF2 was maximally 68% homologous with the large subunit of typical membrane-bound uptake-H₂ases.     

A general method for the transfer of plasmid-borne mutant alleles to the chromosome of Klebsiella pneumoniae using bacteriophage lambda: transfer of pqq genes

Summary A generally applicable method is described for reintroduction of mutant plasmid-borne alleles to the chromosome of Klebsiella pneumoniae using bacteriophage . We, used this method to make stable chromosomal transposon insertions in genes for biosynthesis of pyrroloquinoline quinone in K. pneumoniae     

Molecular cloning and chromosomal location of genes encoding the “Early-methionine-labelled” (Em) polypeptide of Triticum aestivum L. var. Chinese Spring

Summary The Early-methionine-labelled (Em) polypeptide is the most abundant cytosolic polypeptide found in mature wheat embryos. Using a near full-length cDNA clone as a hybridisation probe to detect genomic sequences by Southern blotting of electrophoretic separations of genomic DNA derived from Triticum aestivum L. var. Chinese Spring and a series of its aneuploid derivatives, we demonstrate that the Em polypeptide is the product of a small multigene family in which the copies are located on each of the long arms of the homoeologous group 1 chromosomes. Screening of a variety of genotypes additionally reveals a number of restriction fragment length polymorphisms associated with these loci. Screening of a library of genomic DNA cloned in the vector EMBL 4 has resulted in the isolation of a genomic fragment containing two closely linked Em genes. These are separated by ca. 2.5 kb. Analysis of restriction enzyme digests of this clones fragment has identified it as originating from chromosome 1A.     

Association between dwarfing genes ‘Rht1’ and ‘Rht2’ and resistance toSeptoria tritici Blotch in winter wheat (Triticum aestivum L. em Thell)

Summary Differences in levels of resistance toSeptoria tritici blotch were observed in plants with a specific height-reducing gene. When the gene Rht ₂ was present either as an isoline or in the progeny, a higher degree of resistance was found. The most susceptible plants were observed in populations carrying the Rht ₁ gene. Associations, as determined by phenotypic correlations, were detected betweenSeptoria tritici blotch and tall stature, late heading, and maturity. Plants having short stature, early heading, early maturity, and acceptable levels of resistance were identified in the F₂ population whenRht ₂ was present. Results of this study indicated that wheat breeders must select the appropriate dwarfing source that may confer resistance and grow large F₂ populations, in order to increase the probability of obtaining desired genotypes.     

Functional analysis of a complex oncogene arrangement in biotype III Agrobacterium tumefaciens strains

The ubiquitous grapevine-associated octopine/cucumopine Ti plasmids of biotype III Agrobacterium tumefaciens strains carry two T regions, TA and TB, with a complex oncogene arrangement. Within the octopine/cucumopine group, two main strain types were identified: large TA strains with a TA region resembling the TL region of the biotype I octopine strain Ach5 and small TA strains with a similar T region organization as the large TA strains but with a large internal TA deletion. Structural and functional studies of the representative large TA strain Tm4 revealed six oncogenes. Each oncogene was inserted in a disarmed vector and tested for biological activity using the corresponding oncogenes of Ach5 as standards. Five Tm4 oncogenes, TA-iaaM, T-ipt, T-6b, TB-iaaH and TB-iaaM, were shown to be active, the IS-interrupted TA-iaaH gene was inactive. To study the role of each gene in the pTiTm4 context, several single and multiple pTiTm4 mutations were constructed. It was shown that whereas TA-iaaM and TB-iaaH are essential for tumour formation on grapevine, T-ipt, T-6b and TB-iaaM are not. The avirulence of the TA-iaaM ^- mutant was shown to be due to an inhibitory effect of the T-ipt gene, since a TA-iaaM ^- /T-ipt ^- double mutant was fully virulent. We conclude that the TA-iaaM gene of large TA strains is specifically required to counteract the tumour growth inhibiting activity of the T-ipt gene. Both TA-iaaM and T-ipt are absent from the small TA strains. A model on the roles and interactions of the different oncogenes in large TA and small TA strains is presented.