Genes involved in the biosynthesis of PQQ fromAcinetobacter calcoaceticus

From a gene bank of theAcinetobacter calcoaceticus genome a plasmid was isolated that complements four different classes of PQQ^- mutants. Subclones of this plasmid revealed that the four corresponding PQQ genes are located on a fragment of 5 kilobases. The nucleotide sequence of this 5 kb fragment was determined and by means of Tn5 insertion mutants the reading frames of the PQQ genes could be identified. Three of the PQQ genes code for proteins of M_r 29700 (gene I), M_r 10800 (gene II) and M_r 43600 (gene III) respectively. In the DNA region where gene IV was mapped however the largest possible reading frame encodes for a polypeptide of only 24 amino acids. A possible role for this small polypeptide will be discussed. Finally we show that expression of the four PQQ genes inAcinetobacter lwoffi andEscherichia coli lead to the synthesis of the coenzyme in these organisms.     

Evolution of the T1 retroposon family in the Anopheles gambiae complex

The T1 family of retrotransposable elements is interspersed and moderately repeated in five member species of the Anopheles gambiae sibling-species complex and has diverged little since the radiation of the complex. T1 includes two closely related but independent subfamilies, defined by the presence or absence of linked sets of restriction sites, in all but one species, although the relative abundance of the subfamilies differs within each. Sequence analysis of a 349-bp region from 21 clones isolated from A. gambiae confirmed the bipartite organization by revealing 19 coordinated nucleotide differences between the two subfamilies--T1 alpha and T1 beta. Sequence divergence is not only greater between than within subfamilies, but divergence within T1 beta is less than that within T1 alpha. Between-species comparisons of genomic consensus restriction maps revealed that T1 alpha is fixed for species-diagnostic differences in all species. With one exception, these subfamilies account for approximately 70% of detectable T1 copies in the genome. The results support retroposition as the dominant mechanism underlying the evolution of the T1 family.     

A molecular and cytogenetic survey of major repeated DNA sequences in tomato (Lycopersicon esculentum)

Summary The major families of repeated DNA sequences in the genome of tomato (Lycopersicon esculentum) were isolated from a sheared DNA library. One thousand clones, representing one million base pairs, or 0.15% of the genome, were surveyed for repeated DNA sequences by hybridization to total nuclear DNA. Four major repeat classes were identified and characterized with respect to copy number, chromosomal localization by in situ hybridization, and evolution in the family Solanaceae. The most highly repeated sequence, with approximately 77000 copies, consists of a 162 bp tandemly repeated satellite DNA. This repeat is clustered at or near the telomeres of most chromosomes and also at the centromeres and interstitial sites of a few chromosomes. Another family of tandemly repeated sequences consists of the genes coding for the 45 S ribosomal RNA. The 9.1 kb repeating unit in L. esculentum was estimated to be present in approximately 2300 copies. The single locus, previously mapped using restriction fragment length polymorphisms, was shown by in situ hybridization as a very intense signal at the end of chromosome 2. The third family of repeated sequences was interspersed throughout nearly all chromosomes with an average of 133 kb between elements. The total copy number in the genome is approximately 4200. The fourth class consists of another interspersed repeat showing clustering at or near the centromeres in several chromosomes. This repeat had a copy number of approximately 2100. Sequences homologous to the 45 S ribosomal DNA showed cross-hybridization to DNA from all solanaceous species examined including potato, Datura, Petunia, tobacco and pepper. In contrast, with the exception of one class of interspersed repeats which is present in potato, all other repetitive sequences appear to be limited to the crossing-range of tomato. These results, along with those from a companion paper (Zamir and Tanksley 1988), indicate that tomato possesses few highly repetitive DNA sequences and those that do exist are evolving at a rate higher than most other genomic sequences.     

The respiratory response to heat shock in Neurospora crassa

A sharp decrease in oxygen uptake occurred in Neurospora crassa cells that were transferred from 30 degrees C to 45 degrees C, and the respiration that resumed later at 45 degrees C was cyanide-insensitive. Energization of mitochondria, measured in vivo with fluorescence microscopy and a carbocyanine dye, also declined sharply in cells at 45 degrees C. Electron microscopy showed no changes in mitochondrial complexity; however, the cytoplasm of heat-shocked cells was deficient in glycogen granules.     

Diploids in Microsporum gypseum

The paper studies diploids in dermatophyteMicrosporum gypseum. They were isolated as the more rapidly growing sectors from heterokaryons on minimal medium. They are characterized by their wild morphology, conidiation and growth rate, and they are prototrophic. In their genome they contain all the markers present in both mutant components.     

Pegasus, a small terminal inverted repeat transposable element found in the white gene of Anopheles gambiae

Pegasus, a novel transposable element, was discovered as a length polymorphism in the white gene of Anopheles gambiae. Sequence analysis revealed that this 535 bp element was flanked by 8 bp target site duplications and 8 bp perfect terminal inverted repeats similar to those found in many members of the Tcl family. Its small size and lack of long open reading frames preclude protein coding capacity. Southern analysis and in situ hybridization to polytene chromosomes demonstrated that Pegasus occurs in approximately 30 copies in the genomes of An. gambiae and its sibling species and is homogenous in structure but polymorphic in chromosomal location. Characterization of five additional elements by sequencing revealed nucleotide identities of 95% to 99%. Of 30 Pegasus-containing phage clones examined by PCR, only one contained an element exceeding 535 bp in length, due to the insertion of another transposable element-like sequence. Thus, the majority, if not all, extant Pegasus elements may be defective copies of a complete element whose contemporary existence in An. gambiae is uncertain. No Pegasus-hybridizing sequences were detected in nine other anophelines and three culicines examined, suggesting a very limited taxonomic distribution.