Ligand-induced association of rat lymphocyte membrane proteins with the detergent-insoluble lymphocyte cytoskeletal matrix

There are two classes of membrane protein capping on the basis of ligand requirements. Surface immunoglobulin (Slg), the prototype of the first class, requires a single ligand for cap induction. RT1 (rat histocompatibility proteins) requires two antibodies for cap induction. The lateral mobility of Slg is relatively restricted compared with RT1. These differences may be due to differential interaction with the cytoskeleton. After ligand binding 71% of Slg becomes detergent insoluble and is associated with the lymphocyte cytoskeletal matrix. The insolubilization occurs at 4 degrees C and is not inhibited by sodium azide or cytoskeleton-active drugs. The insolubilized ligand-receptor complex can be solubilized by a cytoskeleton destabilizing buffer. In contrast, only 20% of RT1 becomes associated with the lymphocytic cytoskeleton after ligand binding. The ligand-induced receptor-cytoskeleton interaction influences capping behavior and may play a role in cell activation.     

Mapping and sequencing of a gene from myxoma virus that is related to those encoding epidermal growth factor and transforming growth factor alpha.

Myxoma virus, a Leporipoxvirus and agent of myxomatosis, was shown to possess a gene with the potential to encode an epidermal growth factorlike factor. Its relationship to other members of this family, including the poxvirus growth factors from Shope fibroma virus and vaccinia virus, was analyzed. Alignment of DNA sequences and related open reading frames of myxoma virus and Shope fibroma virus indicated colinearity of genes between these poxviruses.     

A light and electron microscopic study of the quadriflagellate green algaSpermatozopsis exsultans

The green flagellateSpermatozopsis exsultans Korshikov has been studied in culture by light and electron microscopy. The organism is naked, bears four flagella and is conspicuously spirally twisted. The ultrastructure and location of cell organelles (except the flagellar apparatus) has been investigated in detail using an absolute configuration analysis. With the exception of a doubling of the flagella and of the secondary cytoskeletal microtubule system,S. exsultans has the exact same complement of organelles occupying the same relative positions as has been described forS. similis. The two species are therefore correctly placed in the same genus. The usefulness of absolute orientations of cell organelles for green algal taxonomy and phylogeny is stressed.Dedicated to Prof.M. Mix on the occasion of her 60th birthday.     

The potential use of DNA probes to identify and type strains within the Mycobacterium tuberculosis complex

DNA was extracted and purified from 11 strains of Mycobacterium bovis isolated from cattle in Ireland. After digestion with restriction endonuclease PvuII and electrophoresis on an agarose gel, the separated DNA fragments were transferred to a nylon membrane and sequentially hybridized with three DNA probes derived from BCG.
None of the three probes detected restriction fragment length polymorphism (RFLP) within the 11 M. bovis strains, indicating a very close genetic relationship. One probe, pBCG12, detected RFLPs between the M. bovis strains and a reference PvuII digest of DNA from M. tuberculosis R37Rv, confirming that M. bovis and M. tuberculosis are closely related though genetically distinct.     

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.     

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.